Method and apparatus for handling link suspend pulse and silent line state transitions of a network device

ABSTRACT

A method and apparatus for handling data during link suspend pulse and the silent line state of a network device operating in a low power link suspend mode is presented. Accordingly, a new generation of network devices capable of operating in both the full power operational mode of prior art network devices, and a low power “link-suspend” operational mode are presented. The low power “link-suspend” (LS) mode reduces the power consumption of a LAN communications link at the physical layer by eliminating the need to continuously transmit standard idles to maintain link between two linked partners. In the LS mode, a low duty cycle “link-suspend-packet” (LSP) is transmitted between periods of silent line state (SLS). During the SLS, which is a non-data transmission period, the transmitter may be turned off to conserve power therefore preventing the receiver from immediately knowing the phase of an incoming data. Thus, in order to prevent loss of data, the LSPs serve to maintain link and provide information necessary to train the receiver loops so that they can quickly lock onto the incoming data. LSPs are specially constructed so that they can serve as part of the data preamble when the network devices are operating in the link suspend mode. Therefore, the nature of the LSPs is that they are compatible with the standard protocol requirements for data transmission.

This application claims priority of U.S. Provisional Application No.60/380,955 filed on May 15, 2002, entitled “Method and Apparatus forHandling Link Suspend Pulse and Silent Line State Transitions of aNetwork Device,” and of U.S. Provisional Application No. 60/326,520filed on Oct. 2, 2001, entitled “Method and Apparatus for TransparentImplementation of Link-Suspend Capabilities in Network Devices,” and isa Continuation-In-Part of U.S. application Ser. No. 09/676,040, filed onSep. 28, 2000 now U.S. Pat No. 6,795,450, entitled “Method and Apparatusfor Supporting Physical Layer Link-Suspend Operation Between NetworkDevices,” the specifications of which are herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of computer network point to pointdata communications, and more particularly to communications links thatnormally use constant idle bit streams between packet transmissions.

2. Background

a. Communications Networks

There are many different types of networks, network systems, and networkdevices for sharing files and resources or for otherwise enablingcommunication between two or more computers, PCs (personal computers),workstations, telephones, etc. The term “network device”, “network node”or “network component” generally refers to a computer linked to anetwork via a network interface card (NIC), or refers to other devicesor apparatus that perform specialized functions in the network, such asrepeaters, bridges, switches, routers, brouters, to name a few examples.Networks may be categorized based on various features and functions. Forexample, the range of a network refers to the distance over which nodesare distributed, such as local-area networks (LANs) within an office orfloor of a building, wide-area networks (WANs) spanning across a collegecampus, or a city or a state, and global-area networks (GANs) spanningacross national boundaries.

In designing a network, there are a large number of possible networkconfigurations (such as ring, tree, star, hybrid combinations of these,etc.) and communication protocols (such as analog or digital andisochronous or non-isochronous) from which to choose. For example, astar-topology network has data sources and sinks coupled to nodes andthe nodes are coupled to a central hub in a star topology. Each node(which may have one or more data sources and sinks coupled thereto)assembles the data received from the one or more data sources coupled toit into the designated frame template and transmits it to the hub.

Many networks operate in accordance with the OSI (Open SystemsInterconnection) Reference Model, which is a seven-layer model developedby the ISO (International Standardization Organization). The OSIReference Model describes how to interconnect any combination of networkdevices in terms of seven functional layers organized in a hierarchy,and specifies the functions that must be available at each layer. Fromhighest level of the hierarchy to lowest level of the hierarchy, the OSIReference Model includes the Application layer, the Presentation Layer,the Session Layer, the Transport Layer, the Network Layer, the Data-LinkLayer and the Physical Layer.

Network architectures (such as Ethernet, ARCnet, Token Ring, and FDDI)encompass the Data-Link and Physical Layers and represent the mostcommon protocols used. The Data Link layer is responsible forconstructing and transmitting data packets as well as receiving anddeconstructing data packets, both sequences based upon the networkarchitecture being employed. The Data-Link layer provides services forthe various protocols at the Network Layer and uses the Physical Layerto transmit and receive the data packets. In a Local Area NetworkCarrier Sense Multiple Access with Collision Detection (LAN CSMA/CD)implementation according to the Institute of Electrical and ElectronicsEngineers, Inc. (IEEE) Standard 802.3 or 802.3u-1995 (IEEE Standards)(See IEEE 802.3 Standard for Carrier Sense Multiple Access withCollision Detect (CSMA/CD) Access method and Physical LayerSpecifications, 1998 Edition), the Data-Link Layer is divided into twosub-layers, the Logical-Link Control (LLC) sub-layer at the top and theMedia-Access Control (MAC) sub-layer at the bottom. The LLC sub-layerprovides an interface for the Network Layer protocols while the MACsub-layer provides access to a particular physical encoding andtransport scheme of the Physical Layer. The MAC sub-layer is typicallyexecuted by a MAC device that operates at one of several standard clockfrequencies. Similarly, the Physical Layer is typically executed by aPhysical Layer Device (PHY) that is responsible for transmitting andreceiving digital code from a communications media or line, andconverting the digital signals into higher intelligence signals for thedevice MAC.

Several structures and protocols are known for implementing the DataLink (e.g., a MAC) and Physical Layers (e.g., a PHY). Ethernet usingcoaxial, twisted pair or fiber-optic cables operates at 10 megabits persecond (Mbps) (e.g., 10BASE-T, 10BASE-F) while fast Ethernet operates at100 Mbps (e.g., 100BASE-T, 100BASE-FX). ARCnet (Attached ResourceComputer Network) is a relatively inexpensive network structure usingcoaxial, twisted pair or fiber-optic cables operating at 2.5 or 20 Mbps.Token Ring topologies use special IBM cable or fiber-optic cable andoperate between 1 and 16 Mbps. Fast Token Ring operates at 100 Mbps. Anew standard is being developed called ATM (Asynchronous Transfer Mode),which operates at speeds of 25.6 or 155 Mbps, although newer versionsmay operate at even higher data rates. Of course, various other networkstructures are known and available.

Over the years, many networks have been designed to operate in 10BASE-Tprotocol. However, as faster and more sophisticated communication becamepossible through improvements in equipment and technology, it has becomedesirable to provide multi-service protocols which can support botholder protocols, such as 10BASE-T, as well as additional communicationprotocols such as those listed above. This is so that it is notnecessary to replace the entire network and related components with newequipment when upgrading to the newer protocol.

During network communications, the Physical Layer (e.g., a PHY) receivesdata packets from the Data-Link Layer (e.g., a MAC) above it andconverts the contents of these packets into a series of electricalsignals that represent 0 and 1 values in a digital transmission. Thesesignals are sent across a transmission medium to a partner PhysicalLayer at the receiving end of the network link. At the destination, thepartner Physical Layer (e.g., a PHY) converts the electrical signalsinto a series of bit values, which are grouped into packets and passedup to the Data-Link Layer (e.g., a MAC) of the destination device by thePhysical Layer (e.g., a PHY) of the destination partner network device.

b. Prior LAN Systems

FIG. 1 is a block diagram of a typical prior LAN system showing keyfunctional components. It illustrates one of the most common IEEE 802.3Ethernet communications links, which requires two PHY layer devices(e.g., a network interface card (NIC) 112 and a Switch device 114) inorder to communicate. The Switch device comprises a switch 120 connectedto media access controllers (MACs) 116, which are in turn connected toswitch physical layer devices (Switch PHYs) 118, which are connected toa wired link 122. Similarly, the NIC 112 comprises a media accesscontroller (MACs) 116 connected to a NIC physical layer device (NICPHYs) 124, which is also connected to the wired link 122.

The switch device media access controllers (MACs) 116 provide data mediato the switch device physical layer devices (Switch PHYs) 118, which inturn transmit and receive data from the wired link 122. Similarly, theNIC 112 media access controller (MACs) 116 providing data media to theNIC physical layer device (NIC PHYs) 124, which in turn transmits andreceives data from the wired link 122. Thus, by using a communicationslanguage, mode, or protocol that the other “partner” understands, theswitch and NIC are able to “talk” to each other over the “link”.

The wired link 122, or media connecting two PHYs normally consists oftwo twisted-pair cables, with one pair utilized for receiving data andthe other for transmitting data. However, various other appropriatewired link 122 media may be used to connect PHYs, such as coax cable,fiber optic cable, satellite links, cell links, radio waves, etc.

c. Physical Layer Devices (PHYs)

FIG. 2 is a block diagram of a typical prior physical layer device (PHY)200 showing key functional components. The same basic PHY circuits canbe utilized in both a network interface card (NIC), a Switch PHYcircuit, as well as other network devices using various media asdiscussed above. Similarly, a PHY may be implemented either as astandalone single or multi-channel (e.g., 4 PHYs on a chip) device, oran integral component within a higher integrated controller that has PHYdevices. The PHY function may also be implemented using a variety of anintegrated circuit technology. For example, PHY functionality may beprovided through a predominantly analog circuit approach or through useof a digital signal processor.

As shown in FIG. 2, a Media Independent Interface (MII) Registers andInterface Logic component 202 is connected to a transmit PHY functionscomponent 204, and a receiver PHY functions component 206. In turn, thetransmit PHY functions component 204 is connected to transmittercircuits 208. The transmitter circuits 208 are connected to a wired link122. Likewise, the receiver PHY functions component 206 is connected toa normal and fast link pulse and valid frame detector 214, and receivercircuits 210. The receiver circuits 210 are in turn connected to thewired link 122. The transmitter circuits 208 are also connected to anormal and fast link pulse generator 212. The receiver circuits 210 areconnected to a normal and fast link pulse and valid frame detector 214.An auto-negotiation state machine 216 is attached to the normal and fastlink pulse generator 212, and the normal and fast link pulse and validframe detector 214.

As part of the IEEE 802.3 standard, the MII Registers and InterfaceLogic component 202 provides a common interface for connecting the PHY200 with a MAC. The MII is capable of interfacing the PHY with differenttypes of standardized MACs so that different vendors can designstandardized products that will successfully interface.

The transmit PHY functions component 204 controls the transmittercircuits 208, which transmit across the wired link 122. Likewise, thereceiver PHY functions component 206 controls the receiver circuits 210,which receive data from the wired link 122.

The normal and fast link pulse generator 212 provides normal link pulses(NLPs) and fast link pulses (FLPs) used to confirm PHY connection toother “partner” or “remote” PHY's. For example, the PHY normal and fastlink pulse generator 212 will generate NLPs which are then transmittedacross the wired link 122 to tell a remote PHY that the transmitting PHYis still connected (i.e. an “I'm here” signal). Herein, the PHY underdiscussion will be referred to as simply “PHY” and a PHY at the otherend of a link will be referred to as a “partner PHY” or “remote PHY”.Unless stated otherwise, a partner or remote PHY behaves in the samemanner as the PHY described within.

Similarly, the normal and fast link pulse and valid frame detector 214provides normal and fast link detection for confirming a valid link withanother PHY. For example, when NLPs received from the wired link 122 bythe PHY receiver are detected by the normal and fast link pulse andvalid frame detector 214, a valid link with the remote PHY transmittingthe NLPs is confirmed. Thus, for 10-BASE-T communications, theindication to a remote PHY receiving and detecting NLP's is that all iswell on the link. On the other hand, if no pulses are received by anexpecting remote PHY, the link is assumed dead.

The auto-negotiation state machine 216 provides to the pulse generator212 and recognizes from the pulse and frame detector 214, variousparameters used to set up the operational mode of the communicationslink. For instance, the method of communication between two PHYs can beeither half-duplex (receive or transmit only) or full-duplex (receiveand transmit simultaneously). In addition, the auto-negotiation blocksets up other parameters such as the speed of the link (e.g., 10 Mbps,100 Mbps or 1000 Mbps), as well as the type of signaling and encodingschemes used (e.g., 100BASE-T4, 100BASE-T2). The IEEE 802.3 Standardauto-negotiation Section (IEEE Std 802.3, 1998 Ed., Section 28) providesfor negotiation between two network endpoints. For example, the IEEEspecifies protocol used by a linked node and hub to select a linkconfiguration compatible to both endpoints. Thus, the auto-negotiationblock is responsible for negotiating with its remote PHY partner toachieve the desired mode of operation.

The type of pulses used by a PHY to negotiate a link vary depending onthe type of PHY. For example, at power on, an old standard 10BASE-T, 10Mbps capacity PHY will transmit Normal Link Pulses (NLPs). Thus any PHYreceiving NLPs is informed that it is communicating with a 10BASE-Tpartner, and will continue operations in 10BASE-T mode. In 10BASE-Tmode, NLPs are transmitted during link negotiation as well as when thelink is idle (e.g., when no data packets are being transmitted).Consequently, the NLP is known as the “link integrity pulse” or “linktest pulse”.

Newer 10BASE-T PHYs and 100BASE-T PHYs use Fast Link Pulses (FLPs)during link set up. FLPs allow for the passage of auto-negotiationparameters. In addition, FLPs are designed to be interpreted as NLPs bynon-FLP capable PHYs. Thus, to an old 10BASE-T PHY, FLPs used duringlink negotiation will look like NLPs. Conversely, a newer 10BASE-T PHYwill be capable of transmitting and interpreting Fast Link Pulses(FLPs), and hence will be able to detect both 10BASE-T and 100BASE-Tmodes of operation.

FIG. 3 is a waveform diagram of link negotiation pulses showing NLPs andFLPs. Referring to FIG. 3, pulses 302 are sent by both PHYs during linknegotiation. NLPs, typically consist of a pulses 304 sent every 16±8 ms.However, FLPs typically consist of bursts of pulses 306, no more than 2ms in duration, sent every 16±8 ms. Generally, each FLP burst of pulses306 consists of a series of clock and data pulses. The data pulsesusually carry link negotiation data indicating link speed, duplex mode,etc.

Hence, during auto negotiation, higher speed PHYs exchange informationidentifying what type of PHY they are and what their communications modecapabilities are. For instance, at power on, a Fast Ethernet (100BASE-T)capable PHY will startup by pulsing the media line with Fast Link Pulses(FLP) to inform remote PHYs of its existence on the line. A remote PHYwill operate in a similar fashion, pulsing the media line with FLPs.When a return FLP is received by the powered on PHY, that PHY willdetect the FLPs, decipher the data bits encoded therein, and identifythe transmitted parameters. Generally, current systems allow the PHYs to“advertise” in this manner what mode each is capable of. The highestcommon operational mode is then chosen. For example, if one of the PHYsadvertises 10BASE-T full duplex and the other PHY advertises 100BASE-TXfull duplex, the PHY advertising 100BASE-TX will reconfigure itsadvertisements to the lower 10BASE-T full duplex capability.

Also, auto negotiation generally only occurs following a reset, ortypically following a link failure or power up. Thus, once a link hasbeen auto negotiated, the PHYs retain the communications mode agreedupon even though other parameters or modes may change duringcommunications. For instance, to and from a data transmission state andan idle state.

In prior systems, a first PHY must continually transmit a signalwaveform in order to maintain the link with a partner PHY at the otherend for two reasons. First, the partner PHY will assume the link issevered if an identifiable waveform of signal is not received for acertain length of time, and second, the partner PHY receiver may looseits “lock” on the timing of the incoming waveform's bits and thus willnot be able to decipher them. Thus, when data packets are not beingtransmitted over the link to a remote PHY, some other type of signal orpulse must be sent.

The type of pulses used by a PHY in between data packet transmissionsvaries depending on the mode of operation negotiated for that link. Forexample, if the link operational mode is 10BASE-T, a PHY will transmitNormal Link Pulses (NLPs) in between data packets. In this case, eachPHY must continually transmit NLPs between data packets (or FLPs to beinterpreted as NLPs) or the partner PHY will assume the link is severedbecause no identifiable signal has been received for a “timeout” period.

Alternatively, if the link operational mode is 100BASE-T, a PHY willtransmit a stream of “idles” in between data packets. In the 100BASE-Tcase, a PHY must continually transmit the “idles” in order to keep thepartner PHY from assuming the link is severed due to no identifiablewaveform over a “timeout” period, as well as so that the partner PHYreceiver does not loose its “lock” on the timing of the incoming bits.Unlike the slower 10BASE-T mode where there is enough time for thereceiving PHY's circuitry to re-align to the timing of received datapulses, in 100BASE-T mode, it is necessary to fill the “quiet” timebetween data packets with a signal that enables the receiving PHY toremain in synchronization with the data pulses of a received packet.Such synchronization is necessary because at 100 Mbps (100BASE-T mode),there is usually not enough time for the receiving PHY's circuitry tore-align to the timing of newly received data pulses immediatelyfollowing a significant “quiet” period.

For example, for 100BASE-T, the partner PHY receiver must lock onto a125 Mbps bit stream (4 bits are encoded into 5 bits duringtransmission). Thus, the partner PHY receiver must distinguish within 8Nano seconds per pulse bit, whether that bit is a “1” or a “0” (multiplevoltage levels or voltage transitions may be used, for example, in thiscase MLT3 having three voltage levels corresponding to +1, 0, and −1 canbe implemented with a transition to the next voltage level representinga “1” and no transition a “0”). In order to make this distinction, PHYreceivers typically use a Phase Lock Loop (PLL) to tune to thetransmitting PHY's output. The tuned PLL lets the PHY receiver samplethe correct points in the received signal to determine if that locationor bit in the waveform is a “1” or “0”. Further, the receiver PLL iscapable of “drifting” or adapting the time at which it takes a sample,with the drifting timing or “phase” of the received waveformcharacteristics. Thus the PLL is able to sample for “1” or “0”distinctions at optimum waveform locations, even when those locationsdrift.

The PLL recovers the phase or timing of the incoming clock to determinethe timing information of the signal being received. For example, whendigital pulses or bits (1's, and 0's) are being received from the media,the PLL is also receiving a timing pulse signal as well. The timingpulse signal lets the PLL know where the next bit will begin, so the PLLcan sample the waveform at the proper point to distinguish whether a bitis a “0” or a “1”. Thus the PLL knows when to expect the next digitalsignal bit. For example, the timing signal tells the PLL how many (e.g.,2, 3, or more) blank spots (0's) are in the signal between two high bits(1s).

Additionally, to assist the PLL, most receivers use an equalizer toadjust for the characteristics of the incoming line. Various types ofequalizers (e.g., adaptive, fixed, etc.) can be used to balance out theeffect the characteristics of the media have on the incoming signal. Forexample, a twisted pair cable typically experiences an attenuation whichis a function of its length and the frequency of interest. The equalizerwill compensate for the attenuation by creating a frequency dependantgain. This results in a frequency response that is as flat as possible,across the spectrum, for that cable length. Digital signal processor(DSP) based equalizers often use “coefficients” which are a numerictable of information to map the input characteristics of a link.

d. Power Consumption

In a common network environment, the transmitters and receivers at bothends of the associated network link use a cycle template to enable theexchange of data. The cycle template continues to be exchanged even whenthe template contains little or no data. This continuous transmittal ofthe template requires the continual expenditure of transmitter andreceiver power.

Power consumption directly influences the cost of operating the device,limits design possibilities, and is of particular importance if thenetwork component is battery driven. For example, if the network deviceis a lap top computer, the useful operating life of the device is adirect function of battery life.

Additionally, providing support for continuous transmittal of templatesfor an entire multi-service network requires significant individualnetwork device power, as well as overall network power. Hence, thedesire to reduce power consumption in LAN NICs, LAN switch equipment,and other LAN apparatus has resulted in many vendors producing low powerPHY devices. However, as will be explained, there is a limit to theamount of power reduction that is possible with today's implementationof physical layer (PHY) devices.

For example, there are several industry schemes and specificationsdesigned to manage or conserve power in a personal computer (PC)environment by powering certain PC components on and off as necessaryduring PC use. This scheme is generally referred to as Wake-on LAN(WOL), though different vendors may call their particular implementationsomething different.

For instance Microsoft Wake-on LAN™ and Advanced Micro Device's MagicPacket™ are classic examples of such schemes. Likewise, the mostprevalent specifications are Microsoft OnNow™ and the ACPI (See AdvancedConfiguration and Power Interface Specification (ACPI), Version 1.0b,Feb. 2, 1999). There is a provision within these industry defactostandards that supports the ability to remotely wake up or put to sleepa networked PC/workstation using specific types of data packets. Thus,using such a scheme it is possible for a PC to enter a suspended mode,or be put to sleep upon receiving a packet over a network.

WOL wake-up and sleep packets are usually generated by a centralmanagement station that is responsible for managing all thePC/workstations and network devices in a network. WOL may be used simplyto switch machines on or off, or automatically wake them up for softwaremaintenance at night when the machines are not in use. Theseapplications require a NIC to consume very little power, but be capableof waking up as soon as a packet is sent to that NIC over the network.Thus, a WOL capable PC that is connected to a LAN can be “woken up” froma power suspend mode by a wake-up packet received over the network bythe PC's PHY, from a partner network device. Use of such technologyallows network managers to wake up a sleeping PC update the software andthen switch the PC back off.

However, a certain portion of the PC's network device must always stayon to allow the network device to be woken up from a remote location inorder to wake the rest of the PC up. Thus, although a lower power statesfor the overall NIC may be entered in prior systems, in order to allowfor Wake-on LAN capability, it is necessary for the PHY part of the NICto stay fully powered. The fully powered PHY continually transmits andreceives signals, so that a channel is kept open for receiving a “wakeup” packet from a partner network device.

An example of an early WOL scheme is Magic Packet™ from AMD. Similar toa programmable VCR waking up at a certain time to record a show, MagicPacket allows a PC to be woken up from across a network withoutre-booting. A Magic Packet is defined as a standard Ethernet MAC framethat contains the address of the target PC NIC that is to be woken up,repeated 16 times within the packet itself. These 16 instances of thestation's IEEE MAC address are preceded by 6 bytes of FF. Thedestination address field within the MAC frame can be either the addressof the individual station to be woken up or a multicast/broadcastaddress i.e. an address that will be received by the PC's MAC controllerdevice.

For example, Magic Packet gives the following example of a data sequencewithin a Magic Packet for a station with IEEE address ‘112233445566’ as:

-   DA, SA, <misc>, FF, FF, FF, FF, FF, FF, 11, 22, 33, 44, 55, 66, 11,    22, 33, 44, 55, 66, <plus 14 times 11, 22, 33, 44, 55, 66>, <misc>,    CRC.

In another example, the OnNow WOL scheme utilizes a more comprehensivepacket-filtering scheme to detect certain types and protocols carriedwithin a frame. There are three basic types of wake up mechanismsdefined in the OnNow specification:

-   -   Wake up on link status change    -   Wake up on Magic Packet    -   Wake up on match against a predefined byte-frame mask stored        within the MAC device

When in a suspend or sleep mode, the majority of the PC/workstationcomponents are put to sleep, including the main CPU and any networksoftware device drivers that may be interfacing to the LAN adapter.Hence, a WOL capable network device must be capable of looking at apacket and deciding if it is the correct one to wake up thePC/workstation while the rest of the machine is asleep. If the packetcontent is a correct match, then the adapter will produce an interrupt,which invokes the power management software. This in turn will decide ifthe PC/workstation is to be fully woken up, woken up just to deal withthis one request with a low level device driver, or simply ignored.

In current network devices, in order to receive a wake up packet orother signal it is necessary for PHYs to stay fully powered constantlytransmitting on the link between two network devices. As a result, alower power constant idle state has been developed having Idle Symbolsor Pulses that are a specific pattern of low level symbols. Thus,transmission of a continuous waveform can be accomplished in order tohold the link between two PHYs by interlacing data packets with aconstant transmission of such low power idles pulses when datatransmission is suspended. Nevertheless, the constant idle pulse staterequires the PHY transmitter to be fully powered and the PHY is asignificant contributor to the power consumption of network devices,adapters, hubs, and switches.

In prior systems, a PHY must transmit a waveform of continuous normalidles when data packets are not being transmitted in order to keep apartner PHY receiver locked into the signal that the first PHY issending. If the partner PHY receiver fails to detect normal link idles,or data bits for a specified period, the receiver will assume that thelink has been broken and the partner PHY will reset. For example, a FastEthernet 100BASE-TX PHY assuming the link is broken will set its Link OKflag to “false”, enter the no-connect mode, and then beginauto-renegotiation by sending FLPs across the link to determine if itcan adequately re-connect to the partner PHY. Thus, upon receipt of FLPsfrom the PHY, the partner PHY will return FLPs to link with the PHY.However, if a data packet is transmitted to either PHY prior tocompletion of the auto re-negotiation, the data will not be received,but instead will be “lost”.

In relation to power management standards, ACPI defines three levels ofpower down that apply to LAN adapters:

-   -   D0—fully operational    -   D1, D2—various levels of power down (some implementations may        support WOL in the D1/2 states)    -   D3 hot—usually Wake-On LAN state    -   D3 cold—fully powered down with all functional units        non-operational

Thus ACPI network devices operate in Network Device Power States D0, D1,D2, and D3.

In the D0 state, the device, including the PHY is fully powered and canfreely transmit and receive data and/or idles. In the D1 and D2 orintermediate states, the device is less than fully powered, but requiresthe PHY to be fully powered in order to constantly transmit idle frames,even though other components of the NIC may be at less than full power.Note that some ACPI implementations support WOL in the D1 or D2 states.D3 has a “D3-hot” and a “D3-cold” state.

In D3-hot, or what prior systems call the Wake-on LAN state, the PHY isstill powered up and constantly sending idle frames (symbols) because ifthe partner PHY fails to receive idles, it may assume that theconnection has been broken (dead wire, unplugged wire, etc.) and willreset. To reset, the PHY will go to the reconnect state, and will begintransmitting in full power D0 mode (FLPs for 100BASE-T, or NLPs for10BASE-T) to determine if the link has been physically broken, or ifthere was some other error. While in D3-hot, because the PHY istransmitting and receiving, the NIC may be forced back to D0 status bythe partner PHY sending a re-initialization “wake up” packet.

In D3-cold the PHY may be powered down, but its receiver can not thenreceive a “wake up” packet. Thus, the PHY is not able to be woken up inD3-cold, and hence the PHY, NIC, PC, or workstation must bereinitialized or reset locally.

Various power requirements need to be met in the D3 states. For example,in Cardbus NIC applications, the D3-hot state requires no more than 200mA to be drawn in total by the card in the Wake-up state, whereas the D3cold requires no more than 5 mA. The challenge to the systems designersis that typical Fast Ethernet PHY devices today can draw more than100-150 mA when configured in WOL mode, and therefore may exceed the 200mA limitations. This is especially so for multi-function cards, such asLAN and Modem NICs where there are several potentially high powereddevices utilized.

Much of the power consumed by a PHY goes to the transmitter, as it mustbe capable of driving up to 100-meters of category-5 cable and maintainIEEE compliance. Moreover, PHYs are usually over-designed to operatehigher power to compensate for poor line conditions.

Consequently, as shown above, most point-to-point LAN links that existtoday have no method or capacity to shut off their transmitter powerbetween valid data transmissions or during a sleep or suspended state.For example, switching off a PHY's transmitter altogether would resultin the remote partner PHY detecting a loss of link due to the lack of atransmitted signal, NLP, or scrambled idle stream being received by itsreceiver. As a result, the constant idle pulse state requires the PHYtransmitter to be fully powered and the PHY is a significant contributorto the power consumption of network devices, adapters, hubs, andswitches.

Fast Ethernet PHYs have already been designed for low voltage and/or lowpower operation. The overall power consumption of the PHY is reduced byreducing the operational power consumption by using lower voltages.However, there is a physical limit to the amount of power reductionsthat can be made to the PHY without losing IEEE compliance orcompromising reliability.

In the case of standard Fast Ethernet PHY devices, when a NIC is the WOLmode, the PHY has to remain functioning at its full typical idling powereven when little or no data is being transmitted or it will loose thelink. Hence, a PHY capable of turning its transmitter off during quietperiods would save significant power.

In addition, there is no current method of notifying a remote networknode via a simple PHY signaling scheme of the type of schemes a networknode supports or requires when waking from a sleep or suspend state.

SUMMARY OF THE INVENTION

The invention provides a method and apparatus for constructing andhandling link suspend pulses and the silent line state transitions of anetwork device operating in link suspend mode. It applies topoint-to-point data communications links capable of operating in a lowpower link suspend mode.

Accordingly, it is an object of an embodiment of the invention toprovide network devices having a full power operational mode forsupporting the high-bandwidth communication requirement of the standardprotocol (e.g., IEEE 802.3), and a low power “link-suspend” operationalmode for operation when only limited communication is occurring, such aswhen there are fewer data packets being transmitted across the link. Thelow power “link-suspend” (LS) mode reduces the power required by a LANcommunications link at the physical layer by transmitting low duty cycle“link-suspend-packets” (LSPs) instead of continuous idle pulses orsymbols during non-data communication periods. For example, in LS mode,an embodiment of the invention maintains a digital communications linkby sending an LSP between periods of Silent Line State (SLS) to preventthe link from resetting. During the SLS, which is a non-datatransmission period, the transmitter power may be turned off to conservepower and then turned back on when there is need to transmit LSPs ordata. By turning transmitter power off with a low duty cycle, i.e.,between LSP transmissions, the present invention substantially reducesphysical layer device (PHY) power.

Link Suspend Packets are used to maintain the communication link betweenthe link partners. In addition, they provide enough information for thelink suspended devices (e.g., PHYs in SLS) to recover the data clock inorder to lock onto the incoming signal and effectively receive the data.According to an embodiment of the invention, an LSP begins with anunscrambled, predetermined and/or predictable preamble. The use of anLSP with an unscrambled and known preamble allows for easy detection ofLSPs. The LSP may also include a scrambled idle sequence, followed by atermination symbol sequence. The termination symbol sequence ispreferably not a symbol sequence used by the standard protocol. Thescrambled idle sequence provides adequate time for the receiver loops tostabilize in preparation for entering silent line state. In one or moreembodiments, LSPs are specially constructed so that they serve as partof the data preamble when the network devices are operating in the linksuspend mode. Therefore, the nature of the LSPs is that they arecompatible with the standard protocol requirement for data transmission.

In one embodiment, a link suspend capable PHY may be connected to anexisting network of PHY devices without any change to the existingnetwork or devices. An LS capable PHY of the present invention alsooperates in the standard protocol mode (e.g., IEEE 802.3) of the othernetwork devices. Data communicated to an LS capable PHY operating ineither the LS mode or the standard protocol mode may not be lost so longas the link is maintained. Thus, incorporating an LS capable PHY into anexisting network of LS capable and/or non-LS capable PHYs istransparent. Operation in LS mode is negotiated between an LS capablePHY and a remote PHY that is also LS capable. One embodiment supportsnegotiation with a remote link partner to set up LS mode by advertisingoperational mode capabilities between the two network devices.Negotiation allows a PHY to easily detect whether it is connected toanother LS mode capable PHY in order to initiate communication in LSmode. An LS capable PHY may transmit and/or receive in LS mode.Transmitting in LS mode is not negotiated. Thus, a PHY operating in LSmode may unilaterally disable the ability to transmit in LS mode andcommunication will not be lost since the partner PHY is capable ofreceiving in either mode.

One aspect of the invention, in accordance with an embodiment, providesa PHY capable of transmitting and receiving valid data frames whennetwork nodes are in LS, sleep, WOL, or link suspend mode. Thus, theinvention is able to return to a full communications state, from a sleepor suspend state without missing any incoming data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a typical prior LAN system showing keyfunctional components.

FIG. 2 is a block diagram of a typical prior physical layer device (PHY)system showing key functional components.

FIG. 3 is a waveform diagram of link negotiation pulses showing NLPs andFLPs.

FIG. 4 is an illustration of a typical top-level state transitiondiagram of a PHY device in accordance with an embodiment of the presentinvention.

FIG. 5 is an illustration of the power consumption of a Link Suspend PHYoperating during the period between data transmissions.

FIG. 6 is a flow diagram illustrating determination of transmit andreceive states of a PHY connected to a partner PHY, in accordance withan embodiment of the invention.

FIG. 7 is an illustration showing the difference in power consumptionbetween transmissions of standard idles and Link Suspend Packets, inaccordance with an embodiment of the invention.

FIG. 8 is an example of a register bit map of a LS modified MediaIndependent Interface link suspend control and status registers showinglink suspend parameters, in accordance with an embodiment of theinvention.

FIG. 9 is a register bit map of an Auto-Negotiation message Next Pageand example link suspend Next Page code words, in accordance with anembodiment of the invention.

FIG. 10 is a general block diagram illustration of a network PHYmodified for Link Suspend capability, in accordance with an embodimentof the invention.

FIG. 11 is an illustration of the portions of a Link Suspend Packet, inaccordance with an embodiment of the invention.

FIG. 12 is a flow diagram illustrating the handling of data transmissionrequest while in link suspend mode, in accordance with an embodiment ofthe invention.

FIG. 13A shows an example of a data preamble for a PHY operating in theIEEE 802.3 format where data arrives at the MAC of a PHY fortransmission to a partner PHY during scrambled idle.

FIG. 13B is an illustration of the data preamble where transmit enablebecame asserted while an LS mode PHY is in Silent Line State, inaccordance with an embodiment of the present invention.

FIG. 13C is an illustration of the data preamble where transmit enablebecame asserted while an LS mode PHY is transmitting the preamble of theLink Suspend Packets, in accordance with an embodiment of the presentinvention.

FIG. 13D is an illustration of the data preamble where transmit enablebecame asserted while an LS mode PHY is transmitting the scrambled idleportion of the Link Suspend Packets, in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method and apparatus for handlinglink-suspend pulse and silent line state transitions for link suspendoperation of a network device. In the following description, numerousspecific details are set forth to provide a more thorough description ofthe present invention. It will be apparent, however, to one skilled inthe art, that the present invention may be practiced without thesespecific details. In other instances, well known features have not beendescribed in detail so as not to obscure the present invention.Hereinafter, the term “system” is used to refer to a device and/or amethod for performing a function. Also, hereinafter the term “networkdevice”, “network node”, “physical layer device” or “PHY” is used torefer to a network apparatus, network device, network interface card(NIC), network node, network hub, a computer linked to a network via anetwork interface card, voice over Internet Protocol systems, LANtelephone systems, or refers to other devices that perform Internet ornetwork communications specialized functions such as repeaters, bridges,switches, routers, brouters, or any other point to point computercommunications element or portion thereof. Furthermore, the PHY functiondiscussed could be implemented using various appropriate integratedcircuit techniques such as by using a predominantly analog circuitapproach or a digital signal processor (DSP) based approach.

One embodiment of the invention generally applies to computer point topoint data communications links that normally use constant idle bitstreams between packet transmissions. Similarly, an embodiment may alsoapply to the situation where LAN nodes are either idle (i.e. no packetsare being transmitted) or they have entered a sleep or suspended mode ofoperation, such as in a wake-on LAN state. For example, the inventionrelates to the construction and handling of specialized data packets(called link suspend packets) used to maintain communication betweennetwork physical layer devices (PHYs) operating in a low power linksuspend mode. The low power link suspend mode turns transmitter poweroff to save power when not needed for data communication between twolinked PHYs. However, to maintain the communication link, thetransmitter power is periodically turned on in order to send the linksuspend packets to the link partner. The link suspend packets providethe link partner information needed to train its receiver loops in astandby mode so that it won't miss any incoming data.

Hereinafter, the terms “protocol” and the term “mode” shall be used torefer to a method, language, mode, protocol, or system of communication.In the description that follow, the standard IEEE 802.3 communicationprotocol for the 100BASE-TX capable PHY will be used for illustrationpurposes only. It will be apparent to those of skill in the art that themethods and apparatuses described herein may be applied to othercommunications protocols requiring continuous transmission of signalsbetween two network devices to maintain link.

In one embodiment, the invention comprises construction and handling oflink-suspend packets in a Fast Ethernet physical layer device (PHY) inthe 100BASE-TX mode of operation. The invention contemplates a newgeneration of lower power Wake-on LAN (WOL) capable adapters and powerefficient switch or hub equipments that save substantial power overprior generations. The dominant source of power required in a 100BASE-TXdata link is due to the transceiver's requirement to transmit acontinuous carrier. Link Suspend (LS) is a method by which a link ismaintained while allowing the transmitter to be powered down during idleperiods. The Link Suspend state eliminates the need for constanttransmission of scrambled IDLE or similar symbols (i.e., depending onthe requirements of the communications protocol) during IDLE periods andreplaces it with a low duty cycle signal (i.e., LSPs) which serves thepurpose of maintaining the link. LSPs are specially constructed toprovide information necessary to train the receiver loops of a partnerPHY in order to prevent loss of incoming data during low poweroperation.

The Link Suspend concept is expandable to other similar Local AreaNetwork standards, such as 10BASE-T, 100BASE-T2, 100BASE-T4, 1000BASE-Tor X and 802.5 networks (including High Speed Token Ring) where twocommunicating nodes share a common link.

Moreover, the invention may apply to various other appropriate datacommunications links, communications systems between two devices,point-to-point data communications links, and signal transmission andreception systems. For example, the invention can be applied to wirelessnetworks, satellite networks, RF (Radio Frequency) networks, or anyother system where idle transmission periods are filled with non-datacarrying transmissions for the purpose of maintaining a valid link.Similarly, Link suspend can also be used with various other appropriatemedia such as coaxial cable, fiber optic cable, satellite links, celllinks, radio waves, etc.

According to an embodiment, to ensure compatibility with prior PHYdevices, link suspend may be implemented as enhancements to existingfunctional blocks within a PHY that normally uses constant idle bitstreams between packet transmissions. Yet, the invention may be usedwith various other appropriate Physical Layers, PHYs, and networkdevices comprising various other appropriate communications networks.

a. Power Savings

In LAN equipment that exist today most high speed point-to-point LANlinks have no method of shutting off the transmitter power between validdata transmissions or during a sleep/suspended state without causing thelink to reset. Hence, a low power LS mode of operation is described thatfacilitates reduction of overall PHY power consumption at both ends ofthe link when network traffic intensity is reduced.

According to an embodiment, two connected communications nodes may entera low power link suspend mode of operation when both nodes are linksuspend capable. The nodes are able to temporarily suspend operationduring idle transmission periods on the link and can recover to fulloperation without losing network data. This “link suspend” (LS) statemay be in response to a specific request by a host controller wishing toenter a lower power mode of operation and suspend network communicationsuntil a specific network packet or event causes the node and host towake up. In Link Suspend state, two link partners that are both able toimplement the scheme may send low duty cycle Link Suspend Packets (LSPs)back and forth in a complimentary fashion in order to keep the linkoperational between normal data packet transmissions. Note that a PHYwhich is capable of Link Suspend may also be capable of operation in thestandard communications protocol (e.g., IEEE 802.3 defined 100BASE-TX).Depending on configuration, such a PHY may be capable of receiving bothLink Suspend and the standard communications protocol traffic.

According to one embodiment, one, or both, of the linked PHY partners inlink suspend state, may cease continuous transmission of scrambled Idlesymbols, as required to maintain link, in accordance with the defaultcommunication protocol (e.g., IEEE 802.3) and instead transmit low dutycycle Link Suspend Packets (LSPs) between periods of Silent Line State(SLS). SLS is a period when the communication link between the linkedPHY partners is basically silent because there are no signals present onthe media dependent interface (MDI). Therefore, in SLS the linked PHYpartners may shut off their transmitters and receiver loops to conservepower. LSPs serve multiple purposes in the LS mode. For example, LSPsprotect the network from the consequences of simplex link segmentfailures. For instance, by sending a known pattern of LSP, the linkpartners have a periodic confirmation that the link is stilloperational. Secondly, LSPs provide signals for periodicresynchronization of the clock recovery and equalizer circuits. Also,LSPs preserve the link status during idle periods between adjacent LSPs.

Thus, a benefit of the Link Suspend state is to lower consumption ofpower by PHY devices during a period that would normally be composed ofthe scrambled Idle state of the standard protocol. The transmitter needonly be on when needed to send LSPs during the periods when no data isbeing communicated between the PHY partners. Thus, since the ratio ofthe time when the transmitter is on versus off while in the Link Suspendmode may result in significant reduction in the power consumption for aphysical layer device, the system allows both physical layer devices ateach end of the link to save power.

Similarly, LS may also be employed where general power reductions arerequired during quiet times on the LAN. As more networks migrate to 100Mbps at the desktop, the savings become more apparent. For instance, ifthe average power savings are of the order of 90 mA per network device(180 mA per link), then for 3.3V systems, this translates to approx. 300mW per PHY. For a 1000 PC network, this translates to 300 W for the PCNIC PHYs and 300 W for the corresponding switch PHY port, i.e., 0.6 kWtotal.

One embodiment vastly reduces power on a systems wide basis and improvesimplementation of a PC's Advanced Configuration Power managementInterface (ACPI) implementation for LAN capable PCs, along with theMicrosoft OnNow™ Wake-on LAN™ (WOL) network interface cards within thenewer generation of networked personal computers. In addition, the lowerpower consumption on every link in the network reduces networkoperational costs and system cooling requirements.

b. Negotiation of LS Mode

A plurality of PHY devices on a network may be capable of communicatingusing the same standard communication protocol, e.g., IEEE 802.3. Thus,whether or not the PHY devices are LS capable, they are able tocommunicate using the standard IEEE 802.3 protocol when linked. Asdiscussed earlier, PHY devices that are LS capable are also capable ofcommunicating in their standard communications protocol. Therefore, a LScapable PHY device connected to a network of non-LS capable PHY devicesis able to communicate with the non-LS capable PHY devices using thestandard protocol. Thus, in one embodiment, the standard communicationprotocol may be a fallback mode of operation while communication in LSmode is a negotiated solution between link partners. This makes additionof LS capable devices onto a network transparent since if one of thedevices cannot communicate in LS, they simply failback to the standardprotocol mode. Accordingly, LS capable network devices may recognizeother LS network devices through the use of negotiation proceduresduring link initialization (e.g., at power-up or from a no-connectstate). Hence, a low power LS mode of operation may provide fornegotiation or auto-negotiation to advertise available low power modecapabilities allowing a LAN adapter or switch product to add severalunique features. In the case of an ACPI/WOL capable NIC, one advantageis much lower power consumption when the WOL scheme is in use. Thus, itis possible to offer an energy efficient or “green” switch that iscapable of recognizing link-suspend capable adapters and entering acorresponding per port low power mode of operation, significantlyreducing the idle power consumption of the switch.

According to an embodiment, implementing LS in either an ACPI/Wake-OnLAN capable adapter or energy efficient switch is straightforward. Theability of a PHY to operate in Link Suspend mode may be advertised to aremote link partner with a Link Suspend Available (LSAV) bit. A NIC mayhave the LSAV bit enabled as a default, relying on the PHY toautomatically enter the mode based on the auto-negotiation result.During auto-negotiation, the LSAV bit may be received from the linkpartner PHY indicating that the partner is capable of link suspendoperation. Hereinafter, the LSAV bit received from the partner PHY isdesignated LPLSAV (Link Partner LSAV). The PHY may only be allowed toenter Link Suspend State when both itself and the remote PHY haveindicated that they support Link Suspend, i.e., both LSAV and LPLSAV areasserted. Additionally, other embodiments may provide for the mode to beentered only when the adapter wishes to enter link-suspend, e.g., whenthe PC is shutting down and entering a sleep state. Hardware selectionof link-suspend operation may be useful for dumb switch controllers thatdo not have a programmable engine or CPU attached to enable (orconfigure) link-suspend via software.

Additionally, any two network devices may be able to operate in the linksuspend mode if they are capable of transmitting and/or receiving linksuspend packets (i.e., LSP). Note that link suspend packets and linksuspend pulses are used interchangeably in this specification. A linksuspend packet comprises the data sent as a link suspend pulse.

In local area networking equipment that exist today there is no means bywhich a switch or hub PHY may easily detect whether it is connected to asuspended Wake-on LAN adapter in a PC, thus allowing it to enter a lowerpower mode of operation for that port. Thus an additional benefit,according to an embodiment, solves the prior difficulty by providing asimple PHY signaling scheme of notifying a remote network node of thetype of schemes a network node supports or requires when waking from asleep or suspend state, such that the remote node may behaveaccordingly.

Likewise, a third benefit, according to an embodiment, is that linksuspend is defined to be a mode of operation which was agreed to duringnegotiation and is thus not lost so long as both link partners areconnected. Thus, exiting from and re-entering into the LS state may notrequire the two link partners re-negotiate the link. For example, an LSoperating network device which has LS_RX_EN de-asserted may unilaterallyenable or disable LS mode transmit (LS_TX_EN=True, or False), so long asthe partner PHY is LS mode receive enabled (LPLS_RX_EN=True), thustechnically operating in the standard protocol mode when LS_TX_EN=Falseand in LS mode when LS_TX_EN=True. Also, an LS operating PHY may exitthe LS state and re-enter the standard link state (e.g. IEEE 802.3normal mode with continuous idle transmission) without resetting to ano-connect state or re-negotiating the link.

According to an embodiment, a PHY device capable of Link Suspendoperation may operate in various states including an auto-negotiationstate, a Link Suspend (LS) state, a Silent Line State (SLS), and adefault communications protocol state (e.g., IEEE 802.3). FIG. 4 is anillustration of a typical top-level state transition diagram of a PHYdevice in accordance with an embodiment of the present invention. Forthis illustration, the states of a PHY device comprise auto-negotiation410, Link Suspend (LS) state 430, Silent Line State (SLS) 440, and IEEE802.3 communication state 420. When two PHY devices are connected, theyenter the Auto-Negotiation state 410 through path 400 which could befrom a no-connect state, for example. In Auto-Negotiation state 410, theconnected PHYs broadcast their LS capabilities to each other so thatthey can properly configure and enter the correct states of operation.Communication during the auto-negotiation state 410 may be by theNext-Page auto-negotiation function of the IEEE 802.3 specification, forexample. From auto-negotiation state 410, a PHY device may transition toLink Suspend state 430 or IEEE 802.3 state 420. In this illustration,IEEE 802.3 is the default mode of operation. The ability of a PHY deviceof the present invention to operate in both the LS state 430 and IEEE802.3 state 420 makes transparent insertion of the PHY device intoexisting networks possible.

An embodiment of this invention includes the added ability within theauto-negotiation process 410 to exchange capabilities and parametersassociated with link-suspend. Thus, when two link-suspend capable PHYsare first connected or powered on, in addition to the other typicalnegotiation parameters, the PHY's may exchange parameters with eachother to determine if they can support link-suspend. For example, unusedbits in the baseline auto-negotiation or Next Page extensions, asdescribed in the IEEE 802.3 standard, may be used to auto-negotiate linksuspend mode as well.

A link suspend capable PHY may control its ability to advertise supportfor link-suspend via a control bit such as the Link Suspend Available(LSAV) bit, which may be controlled by a higher level device via theMAC. A link partner's ability to support link-suspend mode, determinedduring the auto-negotiation process, may be indicated by the LinkPartner Link Suspend Available (LPLSAV) bit. A PHY may only enable LinkSuspend if both of these flags are active. Auto-negotiation of LinkSuspend mode will be discussed further below.

Transition of the PHY device from auto-negotiation state 410 to IEEE802.3 state 420 follows path 412 which may be satisfied if either orboth PHY device(s) is (are) incapable of operating in the Link Suspendmode of the present invention. That is, when either or both LSAV andLPLSAV are not asserted only the default mode of operation is availableand the PHY transitions through path 412 to the IEEE 802.3 state 420. Ofcourse, PHY devices operating in the IEEE 802.3 state 420 may transitionback to auto-negotiation state 410 via path 421 to re-negotiate the linkif, for example, the link is lost between the communicating PHY devices.Note that there may not be any transitions from the IEEE 802.3 state 420to either Link Suspend state 430 or Silent Line State 440 if linkSuspend Mode was not the negotiated solution. Thus, to enter LS mode (LS430 or SLS 440) from IEEE 802.3 state 420, the PHY returns back toauto-negotiation state 410 to re-negotiate the link with the partnerPHY.

A PHY device may transition from auto-negotiation state 410 to LS state430 via transition path 413 when both PHY devices are capable of linksuspend mode of operation in accordance with an embodiment of thepresent invention. This may be accomplished if both LSAV and LPLSAV bitsare asserted during auto-negotiation, for instance. In LS state 430, thePHY may send periodic, low duty cycle Link Suspend Packets (LSPs) whichmaintains the link and serves other purposes such as providing the linkpartner a periodic confirmation that the link is still operational, andproviding the receiver PHY a signal for periodic resynchronization ofits clock recovery and equalizer circuits.

A PHY device may transition from LS state 430 to auto-negotiation state410, IEEE 802.3 state 420 or SLS 440. PHY devices operating in LS state430 may transition back to auto-negotiation state 410 via path 431 if,for example, link is lost between the communicating PHY devices.Communication may be lost due to power interruption, communicationtimeout (e.g., due to absence of link suspend packets), etc.Communication timeout may occur if, for instance, no LSPs or frameactivity are detected for a period of time which may be an indicationthat a cable has been unplugged or remote link partner has been switchedoff. The timeout limit may be set in the PHY so that each PHY keeps tabof the state of the link. Additionally, transition from any state backto auto-negotiation state 410 may be due to requirements specified inthe appropriate standard (e.g., IEEE 802.3).

A PHY device operating in link suspend mode (e.g., from LS state 430, orSLS 440) may unilaterally decide to revert to operation in the IEEE802.3 state 420 from LS state 430 via transition path 432 (or path 442if operating from SLS 440). A PHY device may transition from LS state430 to SLS state 440 via path 434 upon receiving a transmissiontermination data sequence. A termination data sequence may consist ofany appropriate and unique sequence of data not in conflict with therequirements of the standard protocol (e.g., the symbols /L/L/). ForIEEE 802.3 protocol PHY devices, the /L/L/ symbol sequence is invalidthus is ideal for the termination sequence. It will be apparent to thoseof skill in the art that the termination data sequence could be anygroup of symbols so long as it does not conflict with symbols recognizedfor other purposes by the standard protocol.

While in SLS 440, the PHY device may operate in the low powerconsumption mode of the present invention and may monitor the incomingline for signals that may trigger transition back to LS state 430. Forexample, the PHY device may monitor for a specific incoming datasequence such as “P” which could be a data sequence with a 11011 (i.e.,any data pattern with high transition density) pattern to trigger thereceiver out of a sleep state, or a timing trigger which indicates it istime to transmit a Link Suspend Packet to the link partner thus wakingup the transmitter. Transition to LS state 430 from SLS 440 occurs viapath 443 when a PHY device is ready to transmit a link suspend packet.After transmission, the PHY device may return back to SLS 440 via path434 to conserve power. Thus, an LSP occurs between adjacent periods ofSLS and serves to maintain link and train the receiver loops of thereceiving PHY. During SLS 440, the PHY device is using minimal powerbecause the transmitter and receiver circuits may have been turned off.FIG. 5 is an illustration of the power consumption of a Link Suspend PHYoperating during the period between data transmissions (i.e., duringidle state).

Referring to FIG. 5, block 520 represents the state of the PHY in linksuspend mode and block 510 represents a sample power consumption curve.Of course, the power consumption (i.e. 510) of an LS mode PHY at anygiven time is a function of the state of the PHY and which componentsare switched off when not in use. For instance, when in the SLS 440, thepower consumption is at a reduced level 502 due to the transmitter beingpowered down. For illustrative purposes, power level 500 represents areference no-power consumption state (e.g., PHY is powered off).

When a link suspend packet 530 is transmitted from LS state 430, the PHYpower consumption level jumps from level 502 to level 504. Level 504 isequivalent to that of a non-link suspend capable device transmittingstandard idles. Power level 502 is the power consumption during SilentLine State 440. It shows minimal power consumption because very limitednumber of components of the PHY need be powered during SLS. Devices thatmay benefit from reduced power consumption include but are not limitedto: wake-on LAN, green switches, and portable computers. Power savingsdue to suspension of the transmitter functions alone are estimated to beup to 50% of the entire device power for low bandwidth transmissions.

Note that the invention also contemplates powering down various otherappropriate circuits in addition to or instead of some or all of thetransmitter circuitry during SLS 440. For instance, upon entering SLS440 the transmitter as well as the normal and fast link pulse generator212 and/or transmit PHY functions 204 can be shut down, thus savingpower without causing a renegotiation of the link. Therefore, a PHYdevice operating in SLS 440, in accordance with an embodiment of thepresent invention, may consume significantly less power than a PHYdevice operating in the standard IEEE 802.3 state 420.

Referring back to FIG. 4, operation in SLS 440 may be maintained usingcounters (e.g., digital counters) and so long as the counters do nottime out, SLS 440 is maintained via path 444. The counters may time outif, for example, the transmitting PHY fails to send a link suspendpacket during the allotted timing period. As previously discussed, linksuspend packets are used to maintain link and train the receiver loops(i.e., keep them in phase). Thus, if link is lost when in SLS 440, forexample due to a timeout condition, the PHY may transition back toauto-negotiation state 410 via path 441 or to IEEE 802.3 state 420 viapath 442, depending on the desired implementation.

According to embodiments of the present invention, a Link Suspendcapable PHY may be able to transmit and/or receive in Link suspend mode.The ability to receive link suspend formatted traffic may be negotiatedduring auto-negotiation 410. For instance, the auto-negotiation receivefunction may be used to identify the link partner as being able to meetthe link suspend receive specification if a Link Suspend Receive Enable(LS_RX_EN) bit is set in the Auto-Negotiation Unformatted Next Page ofIEEE 802.3 specification. For consistency, the LS_RX_EN bit receivedfrom the link partner is designated as the Link Partner LS_RX_EN(LPLS_RX_EN) bit.

When a local PHY detects a remote link partner's LS_RX_EN bit isde-asserted (i.e., LPLS_RX_EN=0), it should not transmit LS formattedtraffic to the link partner. A remote link partner, by de-asserting itsLS_RX_EN bit is advertising that it may not be capable of receiving theLS transmitted format data. Thus, the link partner may receive data onlyin the standard protocol (e.g., IEEE 802.3) format. Note that an LScapable PHY may receive data in either the LS format or the standardprotocol format but may only receive LS formatted data if the LS_RX_ENbit is asserted. Therefore, a PHY that sets its LS_RX_EN bit indicatesto a remote link partner that it is capable of receiving Link Suspendformatted traffic. The table below shows the allowed states of a PHYafter Auto-Negotiation is complete and Link Suspend has been enabled(i.e., LSAV=1 and LPLSAV=1).

LS_RX_EN LPLS_RX_EN Allowed States 0 0 Standard format (e.g., IEEE802.3) transmit and receive. 0 1 Receive standard format; and TransmitLink Suspend or standard format. 1 0 Receive Link Suspend or standardformat; and Transmit standard format. 1 1 Receive Link Suspend orstandard format; and Transmit Link Suspend or standard format.

As shown in the table, if both PHYs advertise the ability to receivelink suspend traffic (i.e., LS_RX_EN=1 and LPLS_RX_EN=1), link suspendtraffic may be passed bi-directionally between the PHYs. Since each LScapable PHY is also capable of receiving in the standard protocolformat, the local PHY is also capable of receiving and transmitting datain the standard format when operating in LS mode. Thus, if the remotePHY (i.e., link partner) unilaterally decides to stop transmitting in LSmode, the local PHY can still receive the traffic and no data is lost.In the event that the local PHY advertises the ability to receive linksuspend traffic (i.e., LS_RX_EN=1) but the remote PHY does not (i.e.,LPLS_RX_EN=0), only standard protocol formatted data will be transmittedto the remote PHY from the local PHY. However, the local PHY may receivedata formatted either in link suspend mode or the standard protocolformat from the remote PHY.

Where the local PHY advertises inability to receive link suspend traffic(i.e., LS_RX_EN=0) but the remote PHY advertises the ability to receivein LS mode (i.e., LPLS_RX_EN=1), then LS mode formatted traffic orstandard protocol formatted traffic will be sent to the remote PHY fromthe local PHY. However, the local PHY may only receive data in thestandard protocol format from the remote PHY since it is incapable ofreceiving LS formatted data.

Finally, if neither PHY advertises the ability to receive Link Suspendtraffic (i.e., LS_RX_EN=0 and LPLS_RX_EN=0), operation reverts to theprescribed standard (e.g., IEEE 802.3) for transmit and receive traffic.

In one or more embodiments, the ability of a PHY to transmit in LS modeis controlled by station management (e.g., MAC) through a Link SuspendTransmit Enable (LS_TX_EN) bit. The LS_TX_EN bit may be non-negotiatedso that a PHY configured for Link Suspend may unilaterally decide, atany time, to disable transmission in LS mode and switch to the standardprotocol (e.g., IEEE 802.3) format, without losing link and having tore-negotiate. The remote PHY continues to receive traffic without losingdata since it is capable of receiving data in either format at alltimes. However, local PHY changes to LSAV and LS_RX_EN only take effectduring Auto-Negotiation since they are negotiated bits.

In accordance with an embodiment, station management could unilaterallydisable transmission of LSPs when a particular traffic pattern isdetected which necessitates the change from LSPs to standard idles.Thus, when the ability to transmit LSPs is disabled, the transmittersends carrier (e.g., standard idles and data) as per the prescribedstandard (e.g., IEEE 802.3) and the link partner receives this trafficas per the standard.

Additionally, the invention contemplates unilateral re-enablement ofLink suspend transmission so long as LPLS_RX_EN was previouslynegotiated during auto-negotiation, without requiring a renegotiation ofthe link. Thus, for example, station management could also unilaterallydisable transmission of standard idles and data when a particulartraffic pattern is detected which necessitates the change from standardidles to LSPs. Then, when the ability to transmit standard idles anddata as per the prescribed standard (e.g., IEEE 802.3) is changed to thelink suspend mode, the link partner is able to receive the LS modetraffic.

Embodiments of the invention include various systems for negotiatinglink suspend mode. In one embodiment full auto-negotiation based on aNext Page scheme of IEEE 802.3 is used. In other embodiments,transparent negotiation using a low level signaling scheme may beemployed. Additional embodiments comprise combinations of schemes, suchas, for example, combining a version of full Next Page auto-negotiationwith a transparent negotiation backup.

According to an embodiment of the present invention, link suspendcapability may be negotiated through use of full auto-negotiation basedon Next Page capability. Next Page auto-negotiation may be enabled whena link suspend auto-negotiate (LSAN) control bit is set. For instance,following a reset, if LSAN is set, then the PHY will support the NextPage link suspend auto-negotiation scheme. Note that LSAN may alsodefault to false (zero) following a power on reset, but should not beaffected by a soft reset to support any mode of operation. In addition,embodiments may incorporate hardware control pins to allow the defaultvalue of LSAN to be set to facilitate applications that do not wish touse software to change the LSAN setting (e.g., multi-port PHYs in switchapplications).

For example, in an embodiment, unused bits in the baselineauto-negotiation or Next Page extensions, as described in the IEEE 802.3standard, may be used to auto-negotiate link suspend mode. For instance,after a Fast Ethernet PHY transmits an FLP, if there is a return pulse,the PHY will then pass information identifying what type of PHY it isand what modes it is capable of supporting. Next page auto detection oflink suspend will be explained further below.

c. Transparent Negotiation of Link Suspend Mode

Additionally, according to an embodiment of the present invention, linksuspend capability may be negotiated through transparent auto-detect vialow level signaling. Transparent auto-detect is simple to implement andoffers a basic indication to a remote PHY that a first PHY is capable oflink-suspend. Low level signaling (compatible with the existing Ethernetstandards) from the first PHY takes place following a PHY reset or poweron. This scheme provides a simple method for advertising link suspendability without the need for modification to the currentauto-negotiation standards as discussed above for full auto-negotiationof link suspend mode.

For an embodiment having an auto-negotiation system using both a NextPage scheme and a transparent scheme, transparent mode may still beactive during Next Page auto-negotiation mode, however, any commonparameters setup as a result of the transparent negotiation may beover-ridden by those exchanged during the Next Page auto-negotiationmode. In one such example, transparent auto-detection of link suspend isenabled when the link suspend auto-negotiate (LSAN) control bit is false(default) and auto-negotiation Next Page is also disabled (see below).In this mode, a LS capable PHY will employ a simple transparentsignaling method embedded within the standard FLP or 100BASE-T templatesto signal link-suspend ability to a remote partner. This process willonly occur if the link-suspend available (LSAV) control bit in the LScapable PHY is set. Upon recognizing the embedded LSAV signal from apartner PHY, the LS capable PHY will set its own link partnerlink-suspend available bit (LPLSAV) in order to allow for entry into LSmode.

Link-suspend operation is then enabled once the link-suspend receiveenable bit (LS_RX_EN) is set, indicating that the higher layer devicewishes to enter the link-suspend mode. Setting LS_RX_EN inactive causesthe device to leave link-suspend mode and re-enter IEEE 802.3 standardoperating mode as illustrated in FIG. 4 and discussed in more detailabove.

The benefit of a low level detect mode is that it can work within theframework of the existing IEEE 802.3 auto-negotiation standards withoutthe need for changes to the standard. For example, the low level detectmethod for certain existing series of Fast Ethernet PHY devices andcores will inter-operate fully with existing legacy PHYs in the marketplace today. Thus, systems using current auto-negotiation standards maycomprise LS capable devices that will recognize another LS PHY device asthe remote PHY and enable the link-suspend capability. Furthermore, inan embodiment, the LSAV and LPLSAV flags are used internally by the PHYand are also made available to the MAC or Switch.

Although auto-negotiation according to one embodiment may be used tonegotiate Link Suspend mode, other appropriate methods and/or devicesfor allowing network devices to communicate in link suspend mode mayalso be used. For example, a hardware configuration that causesconnected PHYs that are LS mode capable to automatically try linksuspend mode after the no connect state, by sending a link suspendpacket and listening for a return link suspend packet in order toidentify partner LS capability may be used. Similarly, althoughaccording to the embodiments discussed above, negotiation of LScapability is done during initial link negotiation or after no-connectstate. Negotiation, identification, or entry of LS mode may also beperformed at various other appropriate times. In addition, an embodimentof the invention provides for backwards compatibility, so that the LSPHY can interface with non LS PHYs.

d. Link Suspend Mode

According to an embodiment, after negotiation of LS mode capability, anLS PHY or device has multiple options or modes of operation. Forinstance, the LS capable PHY may enter a Normal mode (e.g. mode of priordevices), or an LS mode of operation. For example, a 100 Mb FastEthernet mode (100BASE-T) PC NIC, may enter Normal IEEE 802.3 modehaving its PHY fully powered, and continually transmitting and receivingnormal Idles and data. Alternatively, the PC NIC may enter a low powerLS mode.

Thus, as shown in FIG. 4, once the auto-negotiation process 410 iscomplete, the PHY may enter a normal operating mode IEEE 802.3 state 420or Link Suspend state 430. While in standard operating mode 420, the PHYreceives standard idles and/or transmits standard idles as per the IEEE802.3 standard. In full duplex mode, both receive and transmit ofstandard Idles can occur simultaneously.

FIG. 6 is a flow diagram illustrating determination of transmit andreceive states of a PHY connected to a partner PHY, in accordance withan embodiment of the invention. As shown in FIG. 6, a PHY and partnerPHY physically connected in block 602, can negotiate a link between them(e.g., at block 604). The physical connection at block 602 may be due toa line disconnect, power cycle, protocol requirement for re-negotiationof link, etc. The negotiation may occur during an auto-negotiationphase, for example. For instance, the PHYs may use the Next-PageAuto-Negotiation function of the IEEE 802.3 specification in order topass parameters between the PHYs. Thus, at block 604, the PHY and thepartner PHY determine each other's configuration with respect to abilityto receive Link Suspend signals.

Using the configuration parameters obtained during link negotiation inblock 604, the PHY determines it's allowed transmit and receiveconfigurations as illustrated in the remaining logic blocks. Forinstance, a determination is made at block 606 whether the PHY and thepartner PHY are link suspend capable (i.e., LSAV and LPLSAV are both setto true). If either PHY is not link suspend capable (i.e., LSAV=0 orLPLSAV=0), then the non LS capable PHY can neither receive nor transmitcommunications that include LSPs thus may not operate in the linksuspend mode. Therefore, both PHYs may revert to the standard protocolmethod of communication. For instance, if the IEEE 802.3 standard isemployed, both PHYs enter the standard idle state at block 608, so thatthe PHY can receive and transmit standard IEEE 802.3 idles and receivedata in standard IEEE 802.3 format at block 610.

However, if at block 606 it is determined that both PHYs are linksuspend capable (i.e., LSAV=1 and LPLSAV=1), then further determinationneed be made whether each will transmit and/or receive in link suspend(LS) format or in standard (e.g., IEEE 802.3) format. First it isdetermined whether the PHY is LS receive enabled (i.e., LS_RX_EN=1) at616. If the PHY is not LS receive enabled (i.e., LS_RX_EN=0), then itwill not receive communications that include LSPs. At block 618, adetermination must be made whether the partner PHY is LS receive enabled(i.e., LPLS_RX_EN=1) in order to properly configure the PHY transmitterfunctions. If it is determined (at block 618) that both the PHY andpartner PHY are not LS receive enabled (i.e., LS_RX_EN=0 andLPLS_RX_EN=0) then they may both enter standard (e.g., IEEE 802.3) idlestate at block 608 and communicate in standard protocol (e.g., IEEE802.3) format at block 610, as neither is able to receive communicationsthat include LSPs. Note that although both PHYs are LS capable, they areboth able to communicate in standard (e.g., IEEE 802.36) format. Alsonote that, in other embodiments, it may be possible for either and/orboth PHYs to change to LS receive enabled after the link has beenestablished, thus allowing either and/or both to operate in LS mode.However, since in some embodiments LS receive enable is negotiatedduring auto-negotiation, LS mode may not be available until the link isre-negotiated.

If the result of the determination at blocks 616 and 618 is that the PHYis not LS receive enabled but the partner PHY is LS receive enabled thenthe PHY's receiver enters standard idle state at block 612 so that itcan receive standard (e.g., IEEE 802.3) idles and data in standard(e.g., IEEE 802.3) format at 614. It is then determined, at block 626,whether the PHY is enabled to transmit link suspend packets (i.e.,LS_TX_EN=1) because a PHY in LS mode may unilaterally and at any timedecide to disable the ability to transmit LSPs. Note that adetermination to transmit or not transmit in LS mode (i.e., block 626)may be done at any time by the PHY after the link is established for anLS mode receive enabled partner PHY. Therefore, if the PHY is LStransmit enabled, it may transmit LSPs and data in LS mode format atblock 628 since the partner PHY is capable of receiving in that format.In this mode of transmission, the PHY may shut down its transmitter andother circuitry when not transmitting LSPs or data to save power.However, if the PHY is not LS transmit enabled, it transmits standardidles and data in standard format (e.g., block 630) since the partnerPHY is capable of receiving standard protocol format data and idles. Inthis mode, the transmitter may not be shut down, but other hardwarefunctions, not being utilized, may be shut down to save power.

If the PHY is LS receive enabled, as determined in block 616, then itcan either receive or transmit communications that include LSPs. Adetermination is made at block 617 whether the partner PHY istransmitting in LS mode. If no, the PHY receiver enters standard idlestate at block 612. Otherwise, the PHY receiver enters Silent Line Stateat block 620 and is available for receiving LSPs and data in LS modeformat at block 622. In this receiver mode of operation, a determinationis made at block 624 whether the partner PHY is LS receive enabledbefore a decision can be made on the mode of transmission of the data tothe partner PHY. If the partner PHY is not LS receive enabled, the PHYtransmits standard idles and data in standard format at block 630.

If the PHY is LS receive enabled (determined in block 616), and thepartner PHY is LS receive enabled (determined in block 624), then thePHY and the PHY partner can receive and transmit communications thatinclude LSPs. It is then determined, at block 626, whether the PHY isenabled to transmit link suspend packets because a PHY in LS mode mayunilaterally decide to disable the ability to transmit LSPs. If the PHYis LS transmit enabled, it may transmit LSPs and data in LS mode formatat block 628 since the partner PHY is capable of receiving in thatformat. In this mode of transmission, the PHY may shut down itstransmitter and other circuitry when not transmitting LSPs or data tosave power. However, if the PHY is not LS transmit enabled, it transmitsstandard idles and data in standard format (e.g., at block 630) sincethe partner PHY is capable of receiving standard format data and idles.In this mode, the transmitter may not be shut down, but other hardwarefunctions, not being utilized, may be shut down to save power.

LS mode may be enabled when LSAV and LPLSAV are active as discussedearlier. The LS_RX_EN and LS_TX_EN discretes may be implemented ascontrol register bits that are set either by a higher layer device, orconfigured using other means such as hardware mode configuration pins onthe PHY device. Also, LS_RX_EN may default to either active or inactivefollowing a reset or power on (of the PHY), for example, depending onthe preference of the higher layer devices or hardware pins. LS_TX_ENand LSAV may preferably default to true to allow operation in LS mode ifother conditions, discussed above for LS mode of operation, are met.

Additionally, embodiments allow LS mode to be applied as permanentoperating mode, or in conjunction with various other network devicemodes, as appropriate. For example, LS mode may be entered, not justduring D3 or WOL power states, but also to reduce power consumptionduring intermediate low power modes such as D1 or D2.

Prior art PHYs send constant idle pulses or symbols to a partner PHYwhen data communications are at a minimum, when in any D0-D3 state, orwhen in any WOL state, in order to tell the partner not to drop the linkjust because no data is being received. Similarly, in an embodiment, anLS network device should be able to “hold” the link by using occasionalLSPs comprising data, idle pulses, or idle symbols, as will be furtherexplained below. However, various other appropriate systems for holdingthe link between LS network devices may also be used.

In an embodiment, in order to detect a removed cable, unplugged cable,broken cable, non-functional partner PHY, or powered-off partner PHY, anLSP receive timer may be implemented that detects if LSPs are beingtimely received. If no LSPs are received from the partner PHY within theperiod defined by the parameter LSP Expiration (LSP_Exp), the link isassumed to be broken. When the link is assumed broken, the PHY will fallback to the Auto-Negotiation state 410, as shown in FIG. 4, or to areset state defined for the PHY device. Furthermore, an internal linkstatus flag, LINK_STATUS, may be active while LSPs are received and thetimer has not timed out, and set to false when no LSPs are received fora period exceeding the allowed time limit of LSP_Exp (i.e. timer hastimed out).

e. Link Suspend Packets

In prior art systems, in order to allow for any future communications,it is necessary for a PHY to stay fully powered, continuallytransmitting data frames interlaced with idle symbols or pulses. Theseidle pulses typically contain a specific pattern of low level symbols,that may require less power to transmit across the media or wire, butare enough to keep the receiver of a partner PHY locked on. Hence inlink suspend mode it is still necessary to keep some type of linkrelationship between the PHY transmitter and the partner PHY receiver.The relationship is maintained with Link Suspend Packets (LSPs) thatcause the partner PHY receiver into holding onto the link. The partnerPHY is capable of sending return LSPs, normal idle pulses, data frames,or a WOL of a “D3-hot” state PHY. Thus, LSPs are sent periodically tokeep the link ready and in “standby” state for further communication,and to keep the link from resetting (e.g. resetting before receiving adata packet).

FIG. 7 is an illustration showing the difference in power consumptionbetween transmissions of standard idles and Link Suspend Packets, inaccordance with an embodiment of the invention. The first waveform ofFIG. 7 shows continuous idle periods and data packets transmissions 710,having Idle Periods 700 interspersed between data Packet Transmissions702 during normal network interface communications. Power consumptionduring idle period 700 is shown in expanded view in waveforms 712, 713,and 714. The second waveform 712 shows power consumption 720 duringtransmission of continuous normal idles of a non-LS PHY where normalidles are continuously transmitted to keep a partner receiver “lockedon”. The third waveform 713 shows power consumption of an LS mode PHYduring Idle Periods 700 which comprises periodic high consumption pulse730 during transmission of Link Suspend Packets (LSPs), and thetransmitter off regions 731 (i.e., during Silent Line State 440) betweenLSP transmissions. The LSPs occur at an LSP period (e.g. LSPPeriod) 732and occur for an LSP width (e.g. LSPWidth) 734. The fourth waveform 714is an overlay of the power consumptions of an LS mode PHY and a non-LSmode PHY (i.e., waveforms 712 and 713 superimposed).

As described earlier, link-suspend pulses (LSPs) are used to replacestandard idles or normal idle transmissions, while in the link-suspendmode. The purpose of the LSPs is to indicate the presence of a validlink to a remote link partner as an alternative to the standardscrambled idle stream, while providing the ability to conserve powerwithin the PHY device and on the physical media.

The average link suspend power (e.g. LSAvPwr 740) consumed by a PHYduring the link suspend idle state (i.e., the period comprising SLS andLSP transmissions) can be calculated by comparing the typical powerconsumption (e.g. TypPwr 742) of a PHY during normal idle state, and theminimal power consumption (e.g. MinPwr 744) of a PHY between linksuspend pulses. Hence, using the definitions for LSAvPwr, TypPwr,MinPwr, LSPWidth, and LSPPeriod given thus far, the power consumptionfor the LS mode PHY in a steady state condition is given by thefollowing equation:LSAvPwr=((TypPwr)*(LSPWidth/LSPPeriod))+((MinPwr)*((LSPPeriod−LSPWidth)/LSPPeriod))

Using example values of 85 microseconds for LSPWidth 734 and 256,000microseconds for LSPPeriod 732, from the equation given above, LSAvPwrcan be calculated as follows:LSAvPwr=((TypPwr)*(85/256085))+((MinPwr)*((256085−85)/256085))LSAvPwr=((TypPwr)*(0.0003))+((MinPwr)*(0.9997))LSAvPwr˜MinPwr

Thus, LSAvPwr is roughly equal to the MinPwr consumption of the PHY whenits transmitter is turned off. For example, assuming a typical PHYconsumes roughly 330 mW during standard idle. Then, during link suspendidle state, from present estimates, the PHY could consume as little as50-70 mW, i.e. an 80-85% reduction in power.

Additionally, for network devices having numerous LS capable PHYs, suchas a switch for example, the power savings will be multiplied by thenumber of LS capable PHYs linked to other partner LS capable PHYs. Thus,for a switch having multiple LS capable PHYs interfaced to multiple LSnetwork devices (NICs for example, each having only a single PHY), theNICs and the switch benefit in an 80-85% power savings for each PHY-PHYlink which enjoys the low power LS mode.

f. LSP Composition

In link suspend mode, the period when no data transmission is occurringbetween the two linked PHY partners comprises transmission of linksuspend packets or pulses (LSPs) between periods of silent line state(SLS). In SLS, it is advantageous for a PHY to shut down components thatare not in use (such as the transmitter and some receiver functions) inorder to conserve power since there is no communication between the PHYpartners. Since it is possible that no signal is present on the line ormedia dependent interface (MDI) during SLS, a receiving PHY has no phaseinformation about an incoming signal. However, the phase of an incomingsignal needs to be acquired for the signal to be properly received.Moreover, if the incoming signal is scrambled, then the seed ofscrambled data need be present for the data to be received anddescrambled. Thus, embodiments of the invention implement periodicbursts or transmission packets (known as LSPs) having a specific natureor structure. These bursts or packets allow for the link suspendeddevices (e.g., PHYs in SLS) to maintain link. In addition, these burstsor packets provide enough information for the link suspended devices(e.g., PHYs in SLS) to recover the data clock so that it can lock ontothe incoming signal. For example, bursts or packets having a specificnature or structure may be passed periodically between the transmitterof one PHY in link suspend mode and the receiver of the link partner PHYin link suspend mode to let the receiver of the link partner PHY knowthat the link is still up and to give the link partner PHY informationso that it can effectively receive data.

In an embodiment, an LSP indicates the presence of a link partner inlink suspend mode to facilitate a lower power mode of operation foreither one or both linked PHYs. The frequency of an LSP can be set toany specific value that can be designed into a PHY. The frequency may befixed or programmable. LSPs may be sent uni-directionally orbi-directionally between a PHY and its link partner. Specificimplementations might require LSPs, for example, to be only sent fromthe PHY on the NIC to the partner PHY on the switch and not in the otherdirection. On the other hand, some implementations might require LSPs tobe sent from both the NIC's PHY and the switch or hub's PHY.

In an embodiment of the invention, LSPs can be implemented a number ofways: from single electrical pulses to bursts comprising standard idles,and/or specially coded symbols. For example, the LSP may comprise ofsome of the unused symbols of a particular coding scheme (such as anyunused symbols in a standard IEEE 802.3 coding scheme) in order todistinguish the LSP from data frames or standard idle patterns, thusmaking LSP detection easier. Also, in one embodiment, it may bedesirable to replace 10BASE-T mode normal link pulses (NLPs) with LSPsthat uses the same pulse type as NLPs but with a longer period.

In an embodiment, for 1000BASE-T, where each of four pairs of signallinks employs a duplex transmission approach, four simultaneouslytransmitted LSPs may be used. Also, an embodiment, may shut down one ormore of the four duplex transmission links during link-suspend idle anduse a fewer number of link pairs, or even a single pair if possible, totransmit LSPs and assure resynchronization of partner LS network devicereceivers.

Referring back to FIG. 7, in an embodiment for a 100BASE-TX link, whenlink-suspend mode is enabled and active, a LS Switch PHY transmitterwill start sending LSPs within the timeframe LSPPeriod 732 less LSPWidth734, following the end of a valid frame 702.

According to an embodiment of the invention, an LSP begins with anunscrambled, predetermined and/or predictable preamble. The use of anLSP with an unscrambled and known preamble allows for easy detection ofLSPs. In an embodiment, the nature of the LSP, allows a receiving PHY toquickly lock its receive clock to incoming data and quickly nibble alignto the incoming data (e.g., the phase of the data signal) so that it canrecover the data.

FIG. 11 is an illustration of the portions of a Link Suspend Packet, inaccordance with an embodiment of the invention. As shown in FIG. 11,each LSP is made up of three parts: a preamble 1102, a scrambled idle1104, and termination symbol 1106. In this illustration, the preambleuses symbols such as “P” and “X”, while the termination uses the “/L/L/”symbols.

In one embodiment, the first 12 symbols of the LSP, i.e., the preamble,are unscrambled. In this illustration, the first 10 symbols are “P”symbols 1110 and the next two symbols are “X” symbols 1112. The “X”symbols are used for resetting the receiver descrambler. The use of anunscrambled preamble sequence allows the receive state machine to nibblealign on a known input stream. Thus, the use of an unscrambled preamblelets the receiver avoid the need to reacquire the scrambler startingseed of the transmitter, which would be necessary if the preamble werescrambled. So, while in link suspend mode, the receive state machineneeds only to monitor for a specific incoming data sequence (e.g., anumber of consecutive “P”s where “P” could be the pattern “11011”). Theunscrambled pattern (e.g., “P”) should have a known transition densityso that it is capable of being easily detected and used.

After nibble aligning using some or all of the “P” symbols, the “X”codes may then be used to unlock the descrambler of the receiver. Then,if the seed of the link partner's transmit scrambler is passed duringauto-negotiation, the receiver can use this seed to quickly recover thepattern of the scrambled idle sequence 1104 which follows preamble 1102.Hence, the use of unscrambled preamble and seed information passedduring auto-negotiation allows the receiver to recover clock and lock toincoming LSP or data so as not to lose any data when coming out of SLS.

Note that, where IEEE 802.3 is the prescribed standard, the use of anunscrambled sequence with 12 symbols to lock the receive clock and alignthe incoming data may be adequate in some embodiments, because 12symbols remain under the maximum of 16 nibbles specified for thepreamble by the IEEE 802.3 standard. Moreover, the first 12 symbols ofthe LSP can be used as the first 12 symbols of the data preamble, insubstitution for the existing IEEE 802.3 standard preamble, therebywhile still providing complete IEEE 802.3 compatibility, information isprovided for locking of the receive clock in order to align to theincoming data.

The invention also contemplates various other appropriate unscrambled,predetermined and/or predictable preambles, comprised of a uniquesequencing of code. For instance, if the receive PLL can be locked withfewer symbols than 12, then fewer symbols can be used. The upper boundof the number of symbols (e.g., 16 for IEEE 802.3) may be set by theallowable number of symbols between TX_EN high and data arrival.Embodiments of the invention allow the LSP and the preamble data to usethe same first 12 symbols; thus reducing the state machine complexity.In addition, the invention can work within the frame definition for datapackets set forth in the IEEE 802.3 or any other standard. Moreover,various embodiment may use LSPs having a fixed length or signal timeperiod of unscrambled preamble, in order to minimize the time requiredfor the receiver to lock to incoming signal. Additionally, variousembodiments may use LSPs comprised of high transition signals forvarious reasons including easy detection.

According to an embodiment, the unscrambled preamble may also serve theimportant purpose of allowing for quick clock recovery. During SLS, thereceiver may not have knowledge of the phase of the signal patterns tobe received. By using a known, unscrambled pattern at the beginning ofthe LSP, the receiver can be designed or operated with this pattern inmind to quickly recover the data clock. Since the receiver can acquireclock by looking at the edges of the incoming signal, the use of a hightransition density symbol for “P” can further augment clock recovery.Thus, the LSP can be uniquely constructed to facilitate fast clockrecovery, nibble alignment, scrambler starting seed detection, receivestate machine control, and signal detection.

Note that the invention also contemplates various other appropriateknown unscrambled preamble patterns in order to allow for clockrecovery. For instance, other patterns which do not have high transitiondensities, are not already known to the receiver (e.g., but arepredictable), or are scrambled may be used. The key is to allow thereceiving PHY receiver which is monitoring a line with no signal, tosuccessfully detect an incoming signal, recover that signal's data(e.g., including clock lock to the phase of the bits and sampling of thedata to align with the sequence of the data words), and de-scramble anyscrambled data segments (e.g., using scrambler seed information).

An alternate embodiment uses a scrambled sequence for the LSP preamble.The receiver can then acquire the descrambler seed using the scrambledLSP. However, a scrambled sequence embodiment may require multiplereceive clocks, since the number of allowed scrambled sequences can beon the order of 10¹¹. In addition, the incoming sequence should havesufficient transitions to allow the receiver to acquire the proper seedinformation in adequate time.

According to an embodiment, scrambled idle 1104 of the LSP may be usedto “retrain” the equalizer loops. Any changes in the incoming signalneed to be accounted for and equalized out by the receiver. Thus, onepurpose of the scrambled IDLE sequence in Link Suspend devices is toallow the equalizers time to decay the DC content imposed on the MDI bythe previous data. The pseudo-random nature of the scrambled IDLE signalallows any offset imposed by the transmitted packet to decay. An examplewould be the changes in the signal due to temperature variations. Thus,the scrambled idle symbols can be used to adjust the equalizer loops tothese changes. For instance, a typical time duration for the scrambledidle would be approximately 100 μs, which translates to greater than10,000 clocks for 100BASE-TX. So, during the 10,000-clock duration ofthe scrambled idle, the receiver has time to adapt to the changes.

Note that the invention also contemplates various other appropriatescrambled idle sequences in order to “retrain” the equalizer loops. Forinstance, other sequences that allow changes in the incoming signal tobe accounted for and equalized out by the receiver may be used.

Also, according to an embodiment, termination symbols 1106 is used toterminate the LSP and reenter SLS. For instance, when the transmittersends the “/L/L/” symbols 1120 (see FIG. 11), the transmitter knows itmay reenter SLS. Hence, upon entering SLS the transmitter as well asother circuitry not required during SLS can be shut down, thus savingpower without causing a renegotiation of the link. Similarly, when thereceiver receives the “/L/L/” symbols, it may take the appropriateaction to prepare for the transmitting PHY's possible re-entry into SLS(e.g., the receiver freezes its equalizer loops).

The invention contemplates using termination portions that are scrambledor unscrambled. Similar to the receiver's unscrambling of the scrambledidle, since the seed of the link partner transmit scrambler can bepassed during auto-negotiation, the receiver can also use the seed toquickly recover the pattern of a scrambled termination portion of theLSP (e.g., 1106) which follows scrambled idle 1104. The receive statemachine, while in link suspend mode, monitors for the “/L/L/” symbols(scrambled or unscrambled). When the termination symbols are detected,the receiver loops are signaled to “freeze”.

Note that the invention also contemplates various other appropriatetermination symbols in order to reenter SLS. For instance, otherscrambled or unscrambled, and/or transition rich or transition baresequences that provide the necessary environment and time for thereceiver to reenter SLS and/or “freeze” the receiver loops may be used.

An alternative embodiment provides for letting the receive state machinemonitor for loss of signal, in order to freeze the loops. Monitoring forloss of signal may lead to an associated delay before entering SLS whichmay be avoided by using appropriate termination symbols.

g. Handling of Data Transmission Request

Embodiments of the invention provide for arrival of data at the LScapable PHY at any time for transmission while the PHY is in linksuspend mode (e.g., in SLS or transmitting LSP). Therefore, the LSP isconstructed such that if Transmit Enable is asserted (TX_EN=True) duringlink suspend operation, e.g., during SLS or LSP transmission, data isnot lost at the transmitting PHY or at the receiving PHY.

FIG. 12 is a flow diagram illustrating the handling of data transmissionrequest while in link suspend mode, in accordance with an embodiment ofthe invention. Data transmission request is signaled by the MAC settinga transmit enable (TX_EN) discrete to true thereby signaling to the PHYtransmitter that it is time to send data to the partner PHY. Thus, sincea LS capable PHY may be in one of several states at any one time, e.g.,the IEEE 802.3 Standard Idle state 420, the LS state 430, or the SLS440, handling of the request to start transmission of data will varydepending on the state of the PHY transmitter. For example, the standardprotocol (e.g., IEEE 802.3) may require data transmission to start nomore than 16 nibbles after TX_EN became true and that certain sequencesof information be sent to the receiver of the partner PHY so that itwill be ready to start receiving the data. An example symbol sequence isshown in FIG. 13A for the IEEE 802.3 standard. In the followingdiscussions, FIGS. 12 and 13A-D will be discussed interchangeably.

FIG. 13A shows an example of a data preamble for a PHY operating in theIEEE 802.3 state 420 where data arrived at the MAC of a PHY fortransmission to a partner PHY during scrambled idle. As shown in FIG.13A, when TX_EN is asserted at 1304 (i.e., during scrambled idle 1308),the PHY transmits the “J” and “K” symbols 1310 as the first two nibbles.Then the PHY transmits the encoding requirement of IEEE 802.3 (e.g.,4B/5B) in the remaining 14 nibbles (e.g., 1312 and 1313) of the datapreamble. For example, the first 12 nibbles (i.e., 1312) of theremaining 14 nibbles are the 4 bit code group “1010” for each nibble,and the last 2 (i.e., 1313) which denote start of data is represented by“AB”. Thus, the 16 nibbles of the IEEE 802.3 data preamble sequence, inthe 5B symbol domain, consists of the two Start-of-Stream Delimiter(SSD) symbols “JK”, followed by 12 symbols of “A” (the encoded “1010”pattern), followed by the Start Frame Delimiter (SFD) symbol sequence“AB”.

A partner PHY receiver monitors the MDI for the transition fromscrambled idle 1308 to the “J” state (i.e., “IJ” transition at thebeginning of 1310), that indicates the link partner's transmit has beenenabled. It then replaces the Start-of-Stream Delimiter (i.e., “JK”)1310 with two decoded “A” symbols, “10101010”. It decodes the remaining12 “A” symbols 1312. Finally, Start of Frame Delimiter (“AB”) 1313,which indicates that what follows is data 1314, is decoded. Thus, thereceiver sees 14 symbols of “A” (i.e., “1010”) followed by “AB” beforearrival of data. The receiver may then assert a Receive Data Valid(RX_DV) bit at any time during the preamble, but no later than the SFD,to tell the transmitter that it is properly receiving data.

However, according to an embodiment, a link suspend capable PHY in linksuspend mode may not transmit the standard preamble (FIG. 13A), sincethe line may be silent prior to the arrival of the preamble to data. Forexample, it is possible that in SLS, the partner PHY's receiver may notsee the “IJ” transition (i.e., SSD) since it is not expecting any data.Moreover, although the PHY's transmitter has no knowledge of the stateof the partner PHY's receiver when in link suspend mode, the PHY shouldbe ready to transmit data at any time to prevent loss of data. Thus,embodiments of the present invention vary the data preamble depending onthe state of the LS mode PHY.

Referring back to FIG. 12, at block 1202, the PHY transmitter enterssilent line state, i.e., a state where the communication line from thePHY transmitter to the partner PHY receiver is silent. In one or moreembodiments, silent line state is normally entered after a PHY receivesthe proper termination symbol sequence, e.g., /L/L/ following ascrambled idle sequence. Note that in this specification, thetermination symbol /L/L/ is referred to interchangeably as the SilentLine Delimiter (SLD) symbol.

At block 1204, a timer (or counter) is started to keep track of the timein silent line state (SLS) (since the PHY may not be in SLS for morethan a fixed duration of time). Generally, the time in SLS may notexceed a Silent Line State Duration (SLSD) time limit, which may beprogrammed into the PHY. The SLSD may be a parameter passed to thepartner PHY during auto-negotiation. Exceeding SLSD while in SLS maycause the partner PHY to declare the link as failed and thus return toauto-negotiation state 410 to re-negotiate the link. Thus, each PHY mustkeep track of its duration in SLS. During silent line state, if the PHYtransmitter detects the assertion of transmit enable (i.e., TX_EN=true)at block 1206, it proceeds to create a data preamble (e.g., at block1240) which comprises the preamble of the LSP as shown in FIG. 13B.

FIG. 13B is an illustration of the data preamble where transmit enable(TX_EN=true) occurred while an LS mode PHY is in Silent Line State, inaccordance with an embodiment of the present invention. The construct ofthe LSP and data preamble transmitted during LS mode should be incompliance with existing standards (e.g., IEEE 802.3) in order to assureproper assertion of the receive data valid (RX_DV) bit by the partnerPHY. Thus, as shown in FIG. 13B, for TX_EN high (e.g., at 1304) duringSLS 1320, the transmitter transmits the preamble that is very similar tothat of the LSP preamble (See FIG. 11), in accordance with an embodimentof the invention. The preamble for data transmitted during LS mode hereconsists of 10 “P” symbols 1322, followed by 2 “X” symbols 1324,followed by scrambled idle (“I”) 1326, followed by the Start-of-StreamDelimiter (“JK”) 1328, and finally “B” 1332. The “X” symbols are specialunscrambled code groups that are used in the LSP to unfreeze thereceiver descrambler. Thus, by detecting the “X” symbols, the receivercan quickly lock to the seed of the link partner's 4B/5B encoder.Similar to the preamble part of a LSP, the “P” and “X” symbols of thepreamble for data transmitted during LS mode are unscrambled to allowfor fast clock recovery, nibble alignment, and descrambler lock by thereceiving PHY. The “P” symbol is a signal with high transition density(“11011”), by sending enough “P” symbols, the receiver, which may missone or two of the symbols because it may need to power up somecircuitry, is able to quickly align and prepare for the remainingincoming code sequences.

The receiving PHY replaces the SSD 1328 with the decoded “AA”(“10101010”), just as a non-link suspend capable PHY would or a LScapable PHY that is not in LS mode (e.g., cases described for FIG. 13A).The SSD 1328 is followed by the symbol “B”, and then data 1314. Becausethe receiver replaces SSD 1328 with the “AA” symbol, the SFD is again“AB”, just as in the case without link suspend (e.g., see FIG. 13A). Thereceive data valid bit (RX_DV) is asserted at the detection of the SFD,as may be the case in the non-link suspend case (e.g., FIG. 13A).

Note that the invention also contemplates various other appropriateknown unscrambled data preamble patterns for transmission of data in LSmode during SLS in order to allow for fast clock recovery, nibblealignment, and descrambler lock by the receiving PHY. For instance,other scrambled or unscrambled sequences that provide the necessaryenvironment and time for the receiver to recover the data clock and thusalign with incoming data during SLS may be used.

Referring back to FIG. 12, at block 1242, the data preamble (FIG. 13B)is transmitted followed by the data at block 1244. Data transmissioncontinues so long as TX_EN remains true (i.e., end of data is notencountered) as determined at block 1246. However, if at block 1246TX_EN becomes false, control is transferred to block 1222 fortransmission of scrambled idle. Transmit enable may become false due toend of data for transmission whereby an End of Stream Delimiter may alsobe transmitted as mandated by the operating standard protocol (e.g.,/T/R/ for IEEE 802.3 standard). At block 1222, since scrambled idle maybe transmitted for a fixed period of time, transmission starts with thefirst nibble of scrambled idle (SI). If during transmission of SI,transmit enable becomes true (e.g., at block 1224), control goes toblock 1226 where the data preamble is generated as shown in FIG. 13D.FIG. 13D is an illustration of the data preamble where transmit enableoccurred while an LS mode PHY is transmitting the scrambled idle portionof a Link Suspend Packet, in accordance with an embodiment of thepresent invention. Note that the preamble shown in FIG. 13D has the samestructure as that in FIG. 13A thus the descriptions are the same. Afterthe preamble is generated in block 1226, control returns to block 1242to transmit the data preamble and then to block 1244 to transmit thedata.

However, if at block 1224, transmit enable is not true, then the nextnibble of SI is transmitted at block 1230. The cycle of SI transmissioncontinues until the last nibble of SI is transmitted. If the last nibbleis not transmitted (as determined in block 1232), then control returnsback to block 1224 to check for transmit enable. This cycle continuesuntil the last nibble of SI is transmitted. After the last nibble ofscrambled idle is transmitted, control goes to block 1234 fortransmission of the termination symbols, i.e., Silent Line Delimiter(SLD) symbols. The SLD may be the same termination symbols used for theLSP. After the termination symbols, the PHY transmitter then returnsback to the silent line state at block 1202.

Returning back to block 1206, if it is determined that TX_EN is false atblock 1206, i.e., transmit enable did not occur when PHY is in SLS, thenthe transmitter remains in SLS so long as the timer value is less thanSilent Line State Duration (SLSD). Thus at block 1208, a check is madewhether timer is greater than or equal to SLSD, if false, the timer isincremented at block 1210 and control returns to block 1206 to continuethe SLS wait. However, if the timer is greater than or equal to SLSD,control goes to block 1212 where the first nibble of the LSP preamble istransmitted. In one or more embodiments, an LSP must be transmitted atthe end of SLSD to prevent link shutdown. Thus, at block 1212, the firstnibble of the LSP preamble is transmitted. At 1214 a determination ismade whether transmit enable is true (i.e., TX_EN=true) during LSPpreamble transmission. If transmit enable is not true, then the nextnibble of the LSP preamble is transmitted in block 1218 followed by adetermination in block 1220 whether the transmitted nibble is the lastnibble of the LSP preamble. If it is the last nibble of the LSPpreamble, control flows to block 1222 to start transmission of scrambledidle as described above. Otherwise, control flows back to block 1214 tocontinue and finish the transmission of LSP preamble.

If, however, at block 1214 a determination is made that transmit enablebecame true (i.e., TX_EN=true) during LSP preamble transmission, controlflows to block 1216 to generate the data preamble as shown in FIG. 13C.

FIG. 13C is an illustration of the data preamble where transmit enable(TX_EN=true) occurred while an LS mode PHY is transmitting the preambleof a Link Suspend Packet, in accordance with an embodiment of thepresent invention. The construct of the LSP and data preambletransmitted during LS mode is in compliance with existing standards(e.g., IEEE 802.3) in order to assure proper assertion of the receivedata valid (RX_DV) bit by the partner PHY. Thus, as shown in FIG. 13C,if TX_EN is true at 1304, which is after the first few nibbles (i.e.,1340) of the LSP preamble has been transmitted, the PHY transmittercontinues transmission of the LSP preamble but notes how many nibbles ofthe preamble were transmitted before transmit enable became true so thatit can create the proper data preamble.

Thus, for instance, if transmit enable is asserted (i.e., TX_EN=true) at1304, which is after the transmitter has sent the first three nibbles(i.e., 1340) of the LSP preamble, then the data preamble createdcomprises the remaining symbols of the LSP preamble (i.e., 1342),followed by a nibble of scrambled idle 1344, followed by theStart-of-Stream Delimiter (SSD) 1346. Following the SSD (i.e., 1346),the transmitter uses enough “A” symbols (i.e., 1348) in place of thenumber of LSP preamble symbols (i.e., 1340) transmitted prior totransmit enable going true. Thus, in FIG. 13C, three “A” symbols (i.e.,1348) are transmitted as padding to the data preamble since the firstthree “P” symbols (i.e., 1340) of the LSP were transmitted prior toTX_EN being asserted at 1304. The data preamble then includes the “B”symbol following the “A” padding symbols such that the last “A” symboland the “B” symbol make up the Start Frame Delimiter (SFD) symbol.

Referring back to FIG. 12, control flows from block 1216 to block 1242where the data preamble is transmitted to the partner PHY. The partnerPHY receiver that sees SSD (i.e., “JK”) 1346, knows that data 1314 iscoming, and replaces the SSD with the decoded “AA” (“10101010”) symbols,just as a non-link suspend capable PHY would or a LS capable PHY that isnot in LS mode (e.g., cases described for FIG. 13A). The receiver parsesthe symbols that follow the SSD (i.e., “JK”), and again uses the “AB”symbol as the SFD. In this case also, RX_DV is asserted with thedetection of the SFD. From block 1242, control continues as previouslydescribed.

Note that the invention also contemplates various other appropriateknown unscrambled data preamble patterns for transmission of data in LSmode during LSP preamble in order to allow for fast clock recovery,nibble alignment, and descrambler lock by the receiving PHY. Forinstance, other scrambled or unscrambled sequences that provide thenecessary environment and time for the receiver to recover clock andalign with incoming data during LSP preamble may be used.

h. LS Modified MII Control and Registers

Embodiments of the invention provide for arrival of data at the LScapable PHY at any time for transmission while the PHY is in linksuspend mode (e.g., in SLS or while transmitting LSPs). Therefore, theLSP is constructed such that if Transmit Enable is asserted (TX_EN=True)during link suspend operation, e.g., during SLS or LSP transmission,data is not lost at the transmitting PHY or at the receiving PHY.

FIG. 12 is a flow diagram illustrating the handling of data transmissionrequest while in link suspend mode, in accordance with an embodiment ofthe invention. Data transmission request is signaled by the MAC settinga transmit enable (TX_EN) discrete to true thereby signaling to the PHYtransmitter that it is time to send data to the partner PHY. Thus, sincea LS capable PHY may be in one of several states at any one time, e.g.,the IEEE 802.3 Standard Idle state 420, the LS state 430, or the SLS440, handling of the request to start transmission of data will varydepending on the state of the PHY transmitter. For example, the standardprotocol (e.g., IEEE 802.3) may require data transmission to start nomore than 16 nibbles after TX_EN became true and that certain sequencesof information are sent to the receiver of the partner PHY so that itwill be ready to start receiving the data. An example symbol sequence isshown in FIG. 13A for the IEEE 802.3 standard. In the followingdiscussions, FIGS. 12 and 13A-D will be discussed interchangeably.

FIG. 13A shows an example of a data preamble for a PHY operating in theIEEE 802.3 state 420 where data arrives at the MAC of a PHY fortransmission to a partner PHY during scrambled idle. As shown in FIG.13A, when TX_EN is asserted at 1304 (i.e., during scrambled idle 1308),the PHY transmits the “J” and “K” symbols 1310 as the first two nibbles.Then the PHY transmits the encoding requirement of IEEE 802.3 (e.g.,4B/5B) in the remaining 14 nibbles (e.g., 1312 and 1313) of the datapreamble. For example, the first 12 nibbles (i.e., 1312) of theremaining 14 nibbles are the 4 bit code group “1010” for each nibble,and the last 2 (i.e., 1313) which denote start of data is represented by“AB”. Thus, the 16 nibbles of the IEEE 802.3 data preamble sequence, inthe 5B symbol domain, consists of the two Start-of-Stream Delimiter(SSD) symbols “JK”, followed by 12 symbols of “A” (the encoded “1010”pattern), followed by the Start Frame Delimiter (SFD) symbol sequence“AB”.

A partner PHY receiver monitors the MDI for the transition fromscrambled idle 1308 to the “J” state (i.e., “IJ” transition at thebeginning of 1310), that indicates the link partner's transmit has beenenabled. It then replaces the Start-of-Stream Delimiter (i.e., “JK”)1310 with two decoded “A” symbols, “10101010”. It decodes the remaining12 “A” symbols 1312. Finally, Start of Frame Delimiter (“AB”) 1313,which indicates that what follows is data 1314, is decoded. Thus, thereceiver sees 14 symbols of “A” (i.e., “1010”) followed by “AB” beforearrival of data. The receiver may then assert a Receive Data Valid(RX_DV) bit at any time during the preamble, but no later than the SFD,to tell the transmitter that it is properly receiving the data.

However, according to an embodiment, a link suspend capable PHY in linksuspend mode may not transmit the standard preamble (FIG. 13A), sincethe line may be silent prior to the arrival of the preamble to data. Forexample, it is possible that in SLS, the partner PHY's receiver may notsee the “IJ” transition (i.e., SSD) since it is not expecting any data.However, although the PHY's transmitter has no knowledge of the state ofthe partner PHY's receiver when in link suspend mode, the PHY should beready to transmit data at any time to prevent loss of data. Thus,embodiments of the present invention vary the data preamble depending onthe state of the LS mode PHY.

Referring back to FIG. 12, at block 1202, the PHY transmitter enterssilent line state, i.e., a state where the communication line from thePHY transmitter to the partner PHY receiver is silent. In one or moreembodiments, silent line state is normally entered after a PHY receivesthe proper termination symbol sequence, e.g., /L/L/ following ascrambled idle sequence. Note that in this specification, thetermination symbol /L/L/ is referred to interchangeably as the SilentLine Delimiter (SLD) symbol.

At block 1204, a timer (or counter) is started to keep track of the timein silent line state (SLS) (since the PHY may not be in SLS for morethan a fixed duration of time). Generally, the time in SLS may notexceed a Silent Line State Duration (SLSD) time limit, which may beprogrammed into the PHY. The SLSD may also be a parameter passed to thepartner PHY during auto-negotiation. Exceeding SLSD while in SLS maycause the partner PHY to declare the link as failed and thus return toauto-negotiation state 410 to re-negotiate the link. Thus, each PHY mustkeep track of its duration in SLS. During silent line state, if the PHYtransmitter detects the assertion of transmit enable (i.e., TX_EN=true)at block 1206, it proceeds to create a data preamble (e.g., at block1240) which comprises the preamble of the LSP as shown in FIG. 13B.

FIG. 13B is an illustration of the data preamble where transmit enable(TX_EN=true) became asserted while an LS mode PHY is in Silent LineState, in accordance with an embodiment of the present invention. Theconstruct of the LSP and data preamble transmitted during LS mode shouldbe in compliance with existing standards (e.g., IEEE 802.3) in order toassure proper assertion of the receive data valid (RX_DV) bit by thepartner PHY. Thus, as shown in FIG. 13B, for TX_EN high (e.g., at 1304)during SLS 1320, the transmitter transmits the preamble that is verysimilar to that of the LSP preamble (See FIG. 11), in accordance with anembodiment of the invention. The preamble for data transmitted during LSmode here consists of 10 “P” symbols 1322, followed by 2 “X” symbols1324, followed by scrambled idle (“I”) 1326, followed by theStart-of-Stream Delimiter (“JK”) 1328, and finally “B” 1332. The “X”symbols are special unscrambled code groups that are used in LS mode tounfreeze the receiver descrambler. Thus, by detecting the “X” symbols,the receiver can quickly lock to the seed of the link partner's 4B/5Bencoder. Similar to the preamble part of a LSP, the “P” and “X” symbolsof the preamble for data transmitted during LS mode are unscrambled.Using an unscrambled preamble allows for fast clock recovery, nibblealignment, and descrambler lock by the receiving PHY. The “P” symbol maybe a signal with high transition density e.g., “11011”. By sendingenough “P” symbols, the receiver, which may miss one or two of thesymbols because it may need to power up some circuitry (while waking upfrom SLS), is able to quickly align and prepare for the remainingincoming code sequences.

The receiving PHY replaces the SSD 1328 with the decoded “AA”(“10101010”) symbol, just as a non-link suspend capable PHY would or anLS capable PHY that is not in LS mode (e.g., cases described for FIG.13A). The SSD 1328 is followed by the symbol “B”, and then data 1314.Because the receiver replaces SSD 1328 with the “AA” symbol, thereceiver sees an SFD that is again “AB”, just as in the case withoutlink suspend (e.g., see FIG. 13A). The receive data valid bit (RX_DV)may then be asserted at the detection of the SFD, as may be the case inthe non-link suspend case (e.g., FIG. 13A).

Note that the invention also contemplates various other appropriateknown unscrambled data preamble patterns for transmission of data in LSmode during SLS in order to allow for fast clock recovery, nibblealignment, and descrambler lock by the receiving PHY. For instance,other scrambled or unscrambled sequences that provide the necessaryenvironment and time for the receiver to recover the data clock and thusalign with incoming data during SLS may be used.

Referring back to FIG. 12, at block 1242, the data preamble (FIG. 13B)is transmitted followed by the data at block 1244. Data transmissioncontinues so long as TX_EN remains true (i.e., end of data is notencountered) as determined at block 1246. However, if at block 1246TX_EN becomes false, control is transferred to block 1222 fortransmission of scrambled idle. At block 1222, since scrambled idle maybe transmitted for a fixed period of time, transmission starts with thefirst nibble of scrambled idle (SI). If during transmission of SI,transmit enable becomes true (e.g., at block 1224), control goes toblock 1226 where the data preamble is generated as shown in FIG. 13D.FIG. 13D is an illustration of the data preamble where transmit enablebecame asserted while an LS mode PHY is transmitting the scrambled idleportion of a Link Suspend Packet, in accordance with an embodiment ofthe present invention. Note that the preamble shown in FIG. 13D has thesame structure as that in FIG. 13A thus the descriptions are the same.After the preamble is generated in block 1226, control returns to block1242 to transmit the data preamble and then to block 1244 to transmitthe data.

However, if at block 1224, transmit enable is not true, then the nextnibble of SI is transmitted at block 1230. The sequence of SItransmission continues until the last nibble of SI is transmitted. Ifthe last nibble is not transmitted (as determined in block 1232), thencontrol returns back to block 1224 to check for transmit enable. Thiscycle continues until the last nibble of SI is transmitted. After thelast nibble of scrambled idle is transmitted, control goes to block 1234for transmission of the termination symbols, i.e., Silent Line Delimiter(SLD) symbols. The SLD may be the same termination symbols used for theLSP. After the termination symbols, the PHY transmitter may then returnback to the silent line state at block 1202.

However, if it is determined that TX_EN is false at block 1206 (i.e.,transmit enable did not occur when PHY is in SLS), then the transmitterremains in SLS so long as the timer value is less than the Silent LineState Duration (SLSD) timer. Thus at block 1208, a check is made whetherthe timer has accumulated time greater than or equal to the SLSD, iffalse, the timer is incremented at block 1210 and control returns toblock 1206 to continue the SLS wait. However, if the timer value isgreater than or equal to the SLSD, control goes to block 1212 where thefirst nibble of the LSP preamble is transmitted. In one or moreembodiments, an LSP must be transmitted at the end of the SLSD toprevent link shutdown. Thus, at block 1212, the first nibble of the LSPpreamble is transmitted. At 1214 a determination is made whethertransmit enable became true (i.e., TX_EN=true) during LSP preambletransmission. If transmit enable is not true, then the next nibble ofthe LSP preamble is transmitted in block 1218 followed by adetermination in block 1220 whether the transmitted nibble is the lastnibble of the LSP preamble. If it is the last nibble of the LSPpreamble, control flows to block 1222 to start transmission of scrambledidle as described above. Otherwise, control flows back to block 1214 tocontinue and finish the transmission of the LSP preamble.

If, however, at block 1214 a determination is made that transmit enablebecame true (i.e., TX_EN=true) during LSP preamble transmission, controlflows to block 1216 to generate the data preamble as shown in FIG. 13C.

FIG. 13C is an illustration of the data preamble where transmit enable(TX_EN=true) became asserted while an LS mode PHY is transmitting thepreamble of a Link Suspend Packet, in accordance with an embodiment ofthe present invention. The construct of the LSP and data preambletransmitted during LS mode should be in compliance with existingstandards (e.g., IEEE 802.3) in order to assure proper assertion of thereceive data valid (RX_DV) bit by the partner PHY. Thus, as shown inFIG. 13C, if TX_EN is true at 1304, which is after the first few nibbles(i.e., 1340) of the LSP preamble has been transmitted, the PHYtransmitter continues transmission of the LSP preamble but notes howmany nibbles of the preamble were transmitted before transmit enablebecame true so that it can create the proper data preamble.

Thus, for instance, if transmit enable is asserted (i.e., TX_EN=true) at1304, which is after the transmitter has sent the first three nibbles(i.e., 1340) of the LSP preamble, then the data preamble createdcomprises the remaining symbols of the LSP preamble (i.e., 1342),followed by a nibble of scrambled idle 1344, followed by theStart-of-Stream Delimiter (SSD) 1346. Following the SSD (i.e., 1346),the transmitter uses enough “A” symbols (i.e., 1348) in place of thenumber of LSP preamble symbols (i.e., 1340) transmitted prior totransmit enable going true. Thus, in FIG. 13C, three “A” symbols (i.e.,1348) are transmitted as padding to the data preamble since the firstthree “P” symbols (i.e., 1340) of the LSP were transmitted prior toTX_EN being asserted at 1304. The data preamble then includes the “B”symbol following the “A” padding symbols such that the last “A” symboland the “B” symbol make up the Start Frame Delimiter (SFD) symbol. Notethat this padding scheme is used in this invention to maintainconsistency in the number of nibbles transmitted between assertion oftransmit enable and data transmission. It should be apparent to those ofskill in the art that the padding may not be necessary so long as thepreamble is adequate to prepare the receiving PHY for the arrival ofdata.

Referring back to FIG. 12, control flows from block 1216 to block 1242where the data preamble is transmitted to the partner PHY. The partnerPHY receiver that sees SSD (i.e., “JK”) 1346, knows that data 1314 iscoming, and replaces the SSD with the decoded “AA” (“10101010”) symbols,just as a non-link suspend capable PHY would or an LS capable PHY thatis not in LS mode (e.g., cases described for FIG. 13A). The receiverparses the symbols that follow the SSD (i.e., “JK”), and again uses the“AB” symbol as the SFD. In this case also, RX_DV may be asserted withthe detection of the SFD. From block 1242, control continues aspreviously described.

Note that the invention also contemplates various other appropriateknown unscrambled data preamble patterns for transmission of data in LSmode during LSP preamble in order to allow for fast clock recovery,nibble alignment, and descrambler lock by the receiving PHY. Forinstance, other scrambled or unscrambled sequences that provide thenecessary environment and time for the receiver to recover clock andalign with incoming data during LSP preamble may be used.

i. LS Modified MII Control and Registers

FIG. 8 is an example of a register bit map of an LS modified MediaIndependent Interface (MII) link suspend control and status registers800 showing link suspend parameters, in accordance with an embodiment ofthe present invention. The LS modified MII comprises a link suspendmessage identification (ID) register 802; link partner status register804; and link suspend control register 806. Each of the three registershas 16 bits (D0 to D15). A “D”, followed by the bit number, identifiesthe bits in the words. The link suspend message identification register802, comprises the Link Suspend Message Identification 830 in bitsD0-10, and reserved bits 828 in bits D1-15. The link partner statusregister 804, comprises reserved bit 828 in bit D0, LPLSAV 826 in bitD1, LPLS_RX_EN 822 in bit D2, reserved bit 828 in bit D3, LPLSPPeriod818 in bits D4-5, LPLSPExp 816 in bits D6-7, LPLSPWidth 812 in bitsD8-11, LPWakeUpCode 808 in bits D12-14, and reserved bit 828 in bit D15(note that the “LP” prefix indicates a link partner). Parameters thatare received during Auto-Negotiation are stored in the link partnerstatus register 804. For example LPLSAV, LPLSPExp, LPWakeUpCode,LPLSPWidth and LPLS_RX_EN. The link suspend control register 806,comprises LS_TX_EN 829 in bit D0, LSAV 824 in bit D1, LS_RX_EN 820 inbit D2, reserved bit 828 in bit D3, LSPPeriod 732 in bits D4-5, LSPExp814 in bits D6-7, LSPWidth 734 in bits D8-11, WakeUpCode 810 in bitsD12-14, and LSAN 807 in bit D15. Reserved bits 828 may be used tosupport redundant codes or data or to perform other valid functions suchas providing message protocol or control information as necessary.

In accordance with one or more embodiments of the invention, duringsystem operation, a PHY in LS mode should ensure that it observes theLink Partner LSPWidth (LPLSPWidth) parameter 812 which it receivedduring negotiation and sets its transmitted LSP pulse width, LSPWidth734, accordingly. The timer-reload value, also referred to as LSPExp814, is set from the parameters received from the remote partner PHY.The link partner LSPExp (LPLSPExp) 816 and link partner LSPPeriod(LPLSPPeriod) 818 values received by a PHY ensure that the LSP receivetimer performs correctly in accordance with the timing of the partnerPHY's transmitter functions.

In the invention, according to an embodiment, the LSPPeriod and LSPWidthvalues are advertised to the link partner during auto-negotiation whenLSAN 807 is set. For PHYs that implement the transparent detect methoddescribed earlier without using the Next Page Auto-Negotiation, thedefault LSP parameter values are assumed (indicated in the Link SuspendCode Word earlier). The link partner should ensure that it observes theLSPWidth parameter received and sets its LSP pulse width accordingly.The same applies to the LS_RX_EN parameter. Thus, the remote PHY uponreceiving LS_RX_EN may set its LSP transmit mode accordingly. Forexample, if the Link Partner LS_RX_EN is false, the PHY should nottransmit LSPs to the partner PHY even though link suspend is in effect.

In an embodiment of the invention, in order to ensure a valid link isstill present, each PHY must implement a counter for timing the arrivalrate of LSPs when link-suspend mode is active. If the timer expires, theflag LINK_STATUS is reset to not OK and the PHY will reset back to theno-connect state (e.g., Auto-Negotiation state 410 of FIG. 4). Both theLSPPeriod 732 and LSPWidth 734 values may be advertised duringauto-negotiation with a link partner.

j. LSP Transmit Only Mode

In an embodiment, it may be desirable or necessary to only have one ofthe PHYs generate LSPs, and the other continue in a non-LS transmitmode. For instance, a PHY generating LSPs may wish to receive 100BASE-TXscrambled idle sequences instead of LSPs. Consequently, the receivecircuits of the PHY receiving the standard idle sequences remain innormal IEEE 802.3 operation and are able to instantly receive a Wake-OnLan (WOL) frame. In order to implement LSP transmit only mode, theLS_RX_EN control flag or bit 820 may be used in Auto-Negotiation NextPage (explained below) to allow a PHY to advertise to its link partnerthat it requires the link partner to always transmit standard idlesequences as opposed to LSPs. Note that setting the LS_RX_EN flag tofalse tells the link partner that the PHY is not able to receive linksuspend pulses. Likewise, the LPLS_RX_EN control flag 822, allows thelink partner to advertise the same requirement in return, if necessary.

According to an embodiment, transmitting LSPs while requesting normalcontinuous idle streams can be used by the LS capable NIC PHYcommunicating with an LS capable Switch PHY, so that an incoming WOLpacket received by the NIC PHY is not missed in 100BASE-TX transmit modedue to the receiver circuits (PLL and equalizer) not being able toquickly lock onto the incoming packet and resynchronize the scrambler.Note that lower power consumption may still be realized in the LSPtransmitting NIC PHY, but not in the normal idle transmitting LS capableSwitch PHY.

k. Next Page Auto-Negotiation of Link Suspend

In an embodiment, during the auto-negotiation state 410, the PHY andpartner PHY may indicate their ability to support link-suspend state 430through Auto-Negotiation Next Page functions. Auto-negotiation Next Pagepermits additional parameters to be exchanged with the remote PHY,allowing reconfiguration of those parameters along with indications ofthe higher layer wake-up modes employed within the node. Use of NextPage requires a simple extension to the IEEE 802.3 Auto-Negotiationstandard to recognize the link-suspend Next Page message ID. Forexample, the message ID may be temporarily set to #20Hex, although otherappropriate values may also be used (e.g., as a result of anystandardization efforts). Further, a control bit may be present toenable or disable the link-suspend auto-negotiation capability describedwithin. As illustrated in FIG. 8, a control bit, Link-SuspendAuto-Negotiation (LSAN) 807, is identified for this purpose. Moreover,PHY Wake Up Code 810 and link partner Wake Up Code 808 can be containedin the registers allowing either PHY to notify the other PHY of the typeof packet the PHY needs to be sent to be woken up (for instance out of aWOL suspended mode).

According to an embodiment, following a reset, if LSAN 807 is set, thenthe PHY will support the Next Page Link Suspend Auto-Negotiation scheme.LSAN 807 may default to off (false) following a power on reset, but maynot be affected by a soft reset to support Next Page auto-renegotiationof LS mode. Hardware control pins may be implemented that allow thedefault value of LSAN to be set to facilitate applications that do notwish to use higher layer software to change this setting (e.g.multi-port PHYs in switch applications).

As mentioned above, a mechanism, referred to herein as Next Page, may beused for passing operational parameters between PHYs during linknegotiation. The IEEE 802.3 Auto-Negotiation standard, as described inIEEE 802.3 Standard for CSMA/CD Access method and Physical LayerSpecifications, Section 28.2.3.4, is one example of such a mechanism,but other valid ones may also be implemented. As governed by theexisting IEEE standard, support of a link-suspend parameter exchangerequires the assignment of a link-suspend Next Page Message ID. Acontrol register, link-suspend message ID (LSMsgID) 830, is identifiedfor setting the Next Page message ID parameter. This may either be ahardwired value within the PHY or a programmable register that may besetup by the controller interfacing to the PHY (e.g., see the LSmodified MII registers above).

FIG. 9 is a register bit map of an Auto-Negotiation message Next Pageand example link suspend Next Page code words, in accordance with anembodiment of the invention. In this example, an unformatted Next Page#1 902, and unformatted Next Page #2 904, are shown following themessage Next Page 900. Here, using the IEEE standard, the Next Pagescheme provides a means of transmitting 16-bit Next Page words (900,902, and 904, either Message or Unformatted Next Pages) to a partnerPHY. Although the Next Page scheme is described here, various otherappropriate combinations of registers may be used for link negotiation.

The Auto-Negotiation Message Next Page 900, comprises a Link SuspendMessage ID (LSMsgID 830) in bits D0-10, and reserved bits 828 in bitsD11-15 for providing message parameters and control (e.g., Next Pageflags). The 11-bit Link Suspend message ID indicates that further pagesto follow provide additional link-suspend code words in the unformattedcode word format.

The unformatted Next Page #1 902, comprises the 11-bit link suspend codeword 920, and reserved bits 828 in bits D11-15 for providing messageparameters and control (e.g. Next Page flags). Similarly, theunformatted Next Page #2 904, comprises the 11-bit link suspend codeword 940, and reserved bits 828 in bits D11-15 for providing messageparameters and control (e.g. Next Page flags).

The link-suspend code word 920, provides the basic parameters used toset up link suspend operation 430. Link-suspend code word 940, isoptionally sent, only if a bit field of the first link-suspend code wordis set, indicating there is further information to be sent. Examples ofparameters sent in the two code words, according to an embodiment, aredescribed below. The bits in the words are recognized by a “D”, followedby the bit number as illustrated in FIG. 9.

Link-suspend Code Word 920 (D0-D10)

-   bit D0=LSAV 824    -   value 0=Link-suspend Not Enabled (but PHY is capable)    -   value 1=Link-suspend Capable (enabled if both link partners are        capable).-   bit D1=LS_RX_EN 820 (receive capability)    -   value 0=PHY can only receive in standard mode only (remote PHY        must ensure that when it sees this it does not transmit LSPs        during link-suspend idle state);    -   value 1=PHY is capable of receiving LSPs.-   bits D2-D3=LSPExp 814 (LSP receive timeout)    -   value 0=2×LSPPeriod value (default)    -   value 1=3×LSPPeriod value    -   value 2=4×LSPPeriod value    -   value 3=off (never times out)-   bits D4-D5=LSPPeriod 732 (LSP pulse spacing)    -   value 0=512 ms (default)    -   value 1=2×512 ms    -   value 2=3×512 ms    -   value 3=4×512 ms-   bits D6-D9=LSPWidth 734 (minimum pulses width required by this PHY    to operate)    -   value 0=16 symbols (default)    -   value n=(n−1)×16 symbols (where n=2-15)        (Optional) Link-suspend Code Word 940 (D0-D10)-   bits D0-D2=WakeUpCode 810 (see examples below)-   bits D3-D10=reserved 828

Note that these are example assignments and values only. Various otherappropriate message, word, and bit combinations may be used for varyingimplementations of link-suspend.

1. Wake-Up Codes

In an embodiment, a PHY may use a second link-suspend code word 940,during auto-negotiation 410, to advertise additional parameters toremote partner PHYs. For example, three bits of Link Suspend Code Word940 may be reserved for indicating the packet required by the node to“wake up” from a sleep state or to perform Wake-On LAN (WOL) operations.The network operating system driver is required in this case to write ameaningful value to the WakeUpCode field 810 of a register within thePHY device. This capability permits an LS Switch PHY to recognize, whichend stations or attached partner LS NIC PHYs are sleep capable, alongwith what packet types or link conditions can be used to wake up eachsleep capable node, without the need or intervention of higher layerprotocols. The switch may use the codes to employ additional filteringschemes (that recognize the appropriate packet required by a sleepingnode) thereby preventing unscreened packets from reaching the endstation unless they meet the WOL criteria (i.e. are the appropriate wakeup packet).

For an embodiment, example Wake-Up codes 810 may be as follows:

-   -   =000 Not defined (NIC—default)    -   =001 Originator of wake up packet (normally a switch port)    -   =010 Wakeup using Link Status change    -   =011 Wakeup using Magic Packet    -   =100 Wakeup using Masked Packet (e.g. OnNow)    -   =101-110—User defined    -   =111—Reserved for future use (e.g. Wake up code expansion        control word in a further link suspend code word)

For this embodiment, a code value of zero simply means the software hasleft the Wake-Up code undefined. Thus, none-zero values are advertisedby a NIC supporting a form of sleep mode that requires a wakeup packetto resume operation. Note that a switch is usually the originator orforwarder of the wake up packet, with WakeUpCode=001. Also, note thatwhere both PHYs WakeUpCodes are non-zero, either node may be woken up ororiginate wake-up frames (e.g. switch-to-switch connections). Thus, thelink-suspend scheme is programmable and facilitates adjustment of keyoperational parameters, such as wake-up codes, to enable fine-tuning tomatch an application's particular needs and intensity of data traffic.

According to an embodiment, an additional benefit of the invention isthat a network manager may poll the switches in a network and determinewhich PC/workstations are currently sleeping, awake or turned offcompletely, by interrogating the switch management information base(MIB), independent of the PC/workstations being awake or not. Here, theLSAV and LPLSAV flags, which are used internally by the PHY, can also bemade available to the MAC or Switch after link negotiation. Thus, theMAC level controller can determine if a link has link suspend-capabledevices by polling a link-suspend available (LSAV) status bit via the LSmodified MII register, and store the result in a MIB register for systemlevel access.

Similarly, an embodiment allows more intelligent and power sensitivenetwork devices (e.g. switch/hub devices) to be manufactured that canrecognize a sleep capable node without the need for higher-levelprotocol support. The recognition may be supported through a low-levelmechanism for passing link power management parameters and WOLoperational modes between WOL capable network devices. In the example ofa PC LAN adapter and a LAN switch or hub device, the switch can simplyread a PHY register (LPLSAV in the LS modified MII) to determine if aremote partner PHY (and NICs) has sleep or WOL capability. Moreover, anembodiment allows a switch receiving enough LSPs to indicate that itsremote partner is asleep, to poll the switch manager to determine whattype of wake up packet to send to wake up the sleeping partner node, byreading the sleeping partner's wake up code register.

m. Invention Construction

FIG. 10 is a general block diagram illustration of a network PHYmodified for Link Suspend capability, in accordance with an embodimentof the invention. As illustrated, a standard PHY requires severalchanges in order to support the additional LS negotiation, mode, andstates. Also, implementing the invention as an enhancement to a standardPHY facilitates backwards compatibility. Thus, FIG. 10 illustrates thehigh level PHY functions that may be modified to create an LS capablePHY from a prior art PHY, e.g., from a typical prior art PHY 200 shownin FIG. 2, to an LS capable PHY 1000 shown in FIG. 10.

FIG. 10 illustrates an embodiment comprising an LS Modified MIIRegisters and Interface Logic component 1002, connected to a LinkSuspend State Machine 1001, a Transmit PHY Functions and LSP Functionscomponent 1004, a Receive PHY Functions and LSP Support Circuitscomponent 1006, and a Modified Auto-Negotiation State Machine with NextPage Link Suspend Support 1016. In turn, the Link Suspend State Machine1001 is also connected to the Transmit PHY Functions and LSP Functionscomponent 1004, a modified LS capable Transmitter Circuits 1008, and theReceive PHY Functions and LSP Support Circuits component 1006. Thetransmit PHY functions and LSP function component 1004, is connected tomodified LS capable transmitter circuits 1008. Likewise, the receive PHYfunctions and LSP support circuits component 1006, is connected to aNormal and Fast Link Pulse and Valid Frame Detector 214, and a modifiedLS capable Receiver Circuits 1010. The modified LS capable transmittercircuits 1008, is connected to a normal and fast link pulse generator212. The modified LS capable receiver circuits 1010, is connected to thenormal and fast link pulse and valid frame detector 214. The modifiedauto-negotiation state machine with Next Page link suspend support 1016is also attached to the normal and fast link pulse generator 212, andthe normal and fast link pulse and valid frame detector 214.

In an embodiment, the link suspend state machine 1001 provides overallcontrol of the link suspend functions of the system. The state machinemay be a standalone state machine as shown in FIG. 10, or integral tothe receive or transmit PHY function components, which may also be statemachines.

Likewise, according to an embodiment, the LS modified MII Registers andInterface Logic component 1002, provides a common interface forconnecting the LS capable PHY 1000 with different types of standardizedMACs so that different vendors can design standardized products thatwill successfully interface with the LS capable PHY. For example,devices supporting the link suspend modes may be pin compatible with theexisting PHY chip devices, allowing products with the existing chipdevices to later upgrade in hardware, or migrate in design to a lowpower LS version in order to support LS mode without hardware or boardlevel changes. However, various other appropriate PHY interfaces, suchas RMII, SMII, GMII, for example, may also be used.

Additional control and status registers 800 may be located in the LSmodified MII registers and interface logic component 1002 to monitor andcontrol link suspend operation. For example, a Link Suspend Control 806,Link Suspend Partner Status 804, and Link Suspend Message ID 802registers may be employed having bit significance as shown in FIG. 8.

Further, in the invention according to one embodiment, the modifiedauto-negotiation state machine and associated logic 1016, may supportrecognition of and provision of various parameters of a link suspendpartner PHY. For example, the modified auto-negotiation state machinewith Next Page link suspend support 1016 may provide pulse width controlto pulse generator 212 and recognize from the frame detector 214,various parameters used to initiate and control communications and linksuspend operations. Thus, the modified auto-negotiation block isresponsible for negotiating with its remote LS capable PHY partner toachieve the desired communication modes.

For instance, the modified auto-negotiation state machine may transferand/or receive parameters that alter the behavior of an LS PHY'sreceiver in order to match the characteristics of a partner LS PHY'stransmitter; or to dictate a specific link-suspend mode necessary forthe an LS PHY's receiver circuits to operate correctly.

The transmit PHY functions and LSP function component 1004, controls themodified LS capable transmitter circuits 1008, which transmit across thewired link 122. Likewise, the receive PHY functions and LSP supportcircuits component 1006, controls the modified LS capable receivercircuits 1010, which receive data from the wired link 122. The normaland fast link pulse generator 212 provides the timing pulses for themodified LS capable transmitter circuits 1008. Similarly, the normal andfast link pulse and valid frame detector 214 provides receipt triggeringfor the modified LS capable receiver circuits 1010.

The modified transmitter function 1004 and associated circuits 1008support the generation of link suspend packets and the ability to savepower when transmitting link suspend packets between periods of silentline state as compared to standard idle state transmissions.Additionally, the transmitter circuit supports switching off of themajority of the powered up circuits between link-suspend pulses (i.e.,during SLS) in order to reduce the average power consumption of the PHYto a minimum, as illustrated in FIG. 7.

Additionally, the modified receiver function 1006 and associatedcircuits 1010: (1) support detection of valid link suspend packets, (2)detects loss of link suspend packets by timing the interval betweenvalid link suspend packets, and (3) recovers from silent line state 440,upon receipt of a valid packet or frame without the loss of the incomingdata.

Although certain embodiments have been described, the invention providesfull inter-operability with prior and current network devices when thelink suspend features are disabled and will only use link suspendfeatures with another network device having some of the similarcapabilities. Thus, connection of an LS capable PHY device in a networkshould be transparent.

The physical layer link suspend operation described above is forpurposes of example only. An embodiment of the invention may beimplemented in any type of network method, apparatus, device, mode,state, in any network environment, or across any network media. Forexample, it may be used as a stand-alone system, or the apparatus may becoupled to other similar apparatus, PHY, or network device across anytype of network (e.g., LAN, WAN, PSTN, Internet, Cable TV, cellular,satellite, etc.), or any combination thereof.

Thus, a method and apparatus for handling link suspend packets andsilent line state transitions of a network device operating in linksuspend mode have been described. Particular embodiments describedherein are illustrative only and should not limit the present inventionthereby. The invention is defined by the claims and their full scope ofequivalents.

1. An apparatus, comprising: a first device of a plurality of networkdevices, each one of said plurality of network devices having a receiverfunction and a transmitter function, said receiver function including adescrambler; a second device of said plurality of network devices; acommunications link coupling said first device to said second devicesuch that said first device and said second device are link partners,said link partners operating in a plurality of communication modes, saidplurality of communication modes including at least a link suspend modeand a standard protocol mode, said standard protocol mode requiringfrequent communication signals between said link partners to maintainsaid communications link, wherein said link suspend mode comprisessending at least one link suspend packet between periods of silent linestate to maintain said communications link between said link partnersduring periods of no data transmission, said at least one link suspendpacket compriing a preamble sequence having a predictable pattern, saidpreamble sequence unlocking said receiver function's descrambler; ascrambled idle sequence for preparing said receiver function for thesilent line state; and a termination sequence for signaling entry intothe silent line state.
 2. The apparatus of claim 1, wherein saidtransmitter function of at least one of said link partners is shut downduring the silent line state.
 3. The apparatus of claim 1, wherein saidreceiver function of at least one of said link partners is shut downduring the silent line state.
 4. The apparatus of claim 1, wherein saidpreamble sequence of said at least one link suspend packet isunscrambled.
 5. The apparatus of claim 1, wherein said preamble sequenceof said at least one link suspend packet is compatible with saidstandard protocol's requirement for data preamble.
 6. The apparatus ofclaim 1, wherein said scrambled idle sequence of said at least one linksuspend packet is compatible with said standard protocol mode.
 7. Theapparatus of claim 1, wherein said termination sequence is not used bysaid standard protocol mode.
 8. The apparatus of claim 1, wherein saidlink partners are communicating in said link suspend mode over saidcommunications link.
 9. The apparatus of claim 8, further comprising atransmit enable signal in said first device to indicate availability ofdata for transmission from said first device to said second device. 10.The apparatus of claim 9, wherein assertion of said transmit enablesignal causes said transmitter function of said first device to send adata preamble followed by said data to said second device.
 11. Theapparatus of claim 10, wherein composition of said data preamble dependson the communication state of said transmitter function of said firstdevice when said transmit enable signal is asserted.
 12. The apparatusof claim 11, wherein the communication state comprises: a standard idlestate; the silent line state; and a link suspend pulse state.
 13. Theapparatus of claim 12, wherein said data preamble comprises saidstandard protocol's preamble when said transmitter function is in saidstandard idle state.
 14. The apparatus of claim 12, wherein when saidtransmitter function is in the silent line state, said data preamblecomprises: said at least one link suspend packet; a scrambled idlesequence; a start of stream sequence; and a start of frame sequence. 15.The apparatus of claim 12, wherein when said transmitter function is insaid link suspend pulse state, said data preamble comprises: theremaining portion of said at least one link suspend packet; a scrambledidle sequence; a start of stream sequence; and a start of framesequence.
 16. A method for handling link suspend pulse and silent linestate transitions of a network device operating in link suspend mode,said method comprising the steps of: connecting a plurality of networkdevices, each one of said plurality of network devices having a receiverfunction and a transmitter function, said receiver function including adescrambler; creating a communications link by coupling a first deviceof said plurality of network devices to a second device of saidplurality of network devices such that said first and second devices arelink partners; configuring said link partners to operate in a pluralityof communication modes, said plurality of communication modes includingat least a link suspend mode and a standard protocol mode; transmittingfrequent communication signals between said link partners to maintainsaid communications link when operating in said standard protocol mode;maintaining said communications link by periodically transmitting linksuspend packets between periods of silent line state when operating insaid link suspend mode, said transmitted link suspend packets serving totrain said receiver functions, wherein each of said link suspend packetscomprises: a preamble sequence having a predictable pattern, saidpreamble sequence unlocking said receiver function's descrambler; ascrambled idle sequence for preparing said receiver function for thesilent line state; and a termination sequence for signaling entry intothe silent line state; and transmitting data packets from said firstdevice to said second device when said data packets become available fortransmission to said second device without losing said data packetsduring transmission.
 17. The method of claim 16, wherein saidtransmitter function of at least one of said link partners is shut downduring the silent line state.
 18. The method of claim 16, wherein saidreceiver function of at least one of said link partners is shut downduring the silent line state.
 19. The method of claim 16, wherein saidpreamble sequence of at least one of said link suspend packets isunscrambled.
 20. The method of claim 16, wherein said preamble sequenceof at least one of said link suspend packets is compatible with saidstandard protocol's requirement for data preamble.
 21. The method ofclaim 16, wherein said scrambled idle sequence of at least one of saidlink suspend packets is compatible with said standard protocol mode. 22.The method of claim 16, wherein said termination sequence is not used bysaid standard protocol mode.
 23. The method of claim 16, wherein saidlink partners are communicating in said link suspend mode over saidcommunications link.
 24. The method of claim 23, further comprising atransmit enable signal in said first device to indicate availability ofdata for transmission from said first device to said second device. 25.The method of claim 24, wherein assertion of said transmit enable signalcauses said transmitter function of said first device to send a datapreamble before sending said data to said second device.
 26. The methodof claim 25, wherein composition of said data preamble depends on thecommunication state of said transmitter function of said first devicewhen said transmit enable signal is asserted.
 27. The method of claim26, wherein the communication state comprises: a standard idle state;the silent line state; and a link suspend pulse state.
 28. The method ofclaim 27, wherein said data preamble comprises said standard protocol'spreamble when said transmitter function is in said standard idle state.29. The method of claim 27, wherein when said transmitter function is inthe silent line state, said data preamble comprises: at least one ofsaid link suspend packets; a scrambled idle sequence; a start of streamsequence; and a start of frame sequence.
 30. The method of claim 27,wherein when said transmitter function is in said link suspend pulsestate, said data preamble comprises: the remaining portion of at leastone of said link suspend packets a scrambled idle sequence; a start ofstream sequence; and a start of frame sequence.